Title: Deprotonations of ternary iminium salts
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Title: Deprotonations of ternary iminium salts
Physical Description: xv, 156 leaves. : illus. ; 28 cm.
Language: English
Creator: Szabo, William Anthony, 1945-
Publication Date: 1974
Copyright Date: 1974
 Subjects
Subject: Aziridine   ( lcsh )
Salts   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Thesis: Thesis -- University of Florida.
Bibliography: Bibliography: leaves 126-130.
General Note: Typescript.
General Note: Vita.
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Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: alephbibnum - 000580746
oclc - 14081012
notis - ADA8851

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DEPROTONATIONS OF TERNARY IMINIUM SALTS


By

WILLIAM ANTHONY SZABO





















A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY










UNIVERSITY OF FLORIDA

1974




























































Copyright 1974
by
William Anthony Szabo

























To Jean















ACKNOWLEDGEMENTS


The author wishes to thank his Chairman, Professor

James A. Deyrup, for suggesting this research problem,

and for his guidance throughout the course of this

investigation. The author also wishes to express his

sincere appreciation to Drs. W. R. Dolbier, Jr., M. J.

Fregly, L. G. Gramling, R. W. King,.and G. J. Palenik,

for their contributions to his education at the University

of Florida.

The author is indebted to Matt Betkouski, Jim Gill,

Emmett McCaskill, Jeff Staffa, and the other members of

his research group for their friendship, advice, and

assistance.

The author's parents have been an important influence

on his life, and they are deeply thanked for their love

and understanding.

Appreciation is also extended to Mrs. Carolyn Grantham,

who demonstrated not only expertise as a typist, but

infinite patience and cooperation.

Finally, the author wishes to extend special thanks

to Miss Jean L. Muthard, whose companionship and en-

couragement during the course of this research will always

be remembered.
















TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS... ......... ........................ iv

LIST OF TABLES. ........ ......... ....................xiii

ABSTRACT..... ........ ................................. xiv

CHAPTER I APPLICATIONS TO THE SYNTHESIS OF
AZIRIDINES......................................... 1

Introduction..................................... 1

Ketiminium Salts ....... .... ..................... 7

Aldiminium Salts...... .......................... 20

CHAPTER II APPROACHES TO THE SYNTHESIS OF THE
2-AZIRINE SYSTEM............... ..................... 43

Introduction..................................... 43

The Aziridine Approach .......................... 52

The l-Azirine Approach .......................... 57

CHAPTER III EXPERIMENTAL ............................ 64

General Procedure for the Preparation of
the Ketimines (9) ............................ 65

N-(Benzhydrylidene)tert-butylamine (9a) ......... 66

N-(Benzhydrylidene)methylamine (9b) .............. 66

N-(Benzhydrylidene)allylamine (9c) .............. 66

N-(Benzhydrylidene)benzhydrylamine (9d) ......... 67

N-(Benzhydrylidene)aniline (9e) ................. 67

N-(Fluorenylidene)methylamine (18a) ............. 68

N-(Fluorenylidene)tert-butylamine (18b) ......... 68









CHAPTER III EXPERIMENTAL (Continued) Page

General Procedure for the Preparation of
the Ketiminium Salts (12 and 13) ............. 68

N-(Benzhydrylidene)methyl-tert-butylaminium
Fluorosulfonate (12a) ........................ 69

N-(Benzhydrylidene)methyl-tert-butylaminium
Triflate (13a) ............................... 70

N-(Benzhydrylidene)dimethylaminium Fluoro-
sulfonate (12b) .............................. 70

N-(Benzhydrylidene)methylallylaminium Fluoro-
sulfonate (12c) .............................. 71

N-(Benzhydrylidene)methylbenzhydrylaminium
Fluorosulfonate (12d) ........................ 71

N-(Benzhydrylidene)methylanilinium Fluoro-
sulfonate (12e) .............................. 72

N-(Fluorenylidene)dimethylaminium Fluoro-
sulfonate (19a) .............................. 73

Pyrolysis of N-(Benzhydrylidene)methyl-tert-
butylaminium Triflate (13a). N-(Benz-
hydrylidene)methyliminium Triflate (17) ...... 73

Attempted Alkylation of N-(Fluorenylidene)-
tert-butylamine (18b) with Methyl Fluoro-
sulfonate (lla). N-(Fluorenylidene)tert-
butyliminium Fluorosulfonate (19b) ........... 74

Attempted Alkylation of N-(Benzhydrylidene)-
tert-butylamine (9a) with Ethyl Triflate.
N-(Benzhydrylidene)tert-butyliminium
Triflate (20)................................. 74

Pyrolysis of N-(Benzhydrylidene)tert-butyl-
iminium Triflate (20). N-(Benzhydrylidene)-
iminium Triflate (21) ........................ 75

Treatment of N-(Benzhydrylidene)tert-butyl-
iminium Triflate (20) with Aqueous Base.
N-(Benzhydrylidene)tert-butylamine (9a) ...... 76

Treatment of N-(Benzhydrylidene)methyl-tert-
butylaminium Fluorosulfonate (12a) with
n-Butyllithium (23) ......... .. ................... 76

Treatment of 12a with 1,8-Bis(dimethylamino)-
naphthalene (24) ............................. 77









CHAPTER III EXPERIMENTAL (Continued) Page

Treatment of 12a with Lithium 2,2,6,6-
Tetramethylpiperidide (25)................... 78

Treatment of 12a with Lithium 2,6-Di-tert-
butylphenoxide (26) .......................... 78

Treatment of 12a with Sodium Dimsylate (27)..... 79

Treatment of 12a with Potassium tert-Butoxide
(28) in Hexamethylphosphoramide.............. 80

Treatment of 12a with Potassium tert-Butoxide
(28) in Ether................................. 81

Preparation and Titration of a Solution of
Potassium tert-Heptoxide (29) in Xylene...... 81

Treatment of 12a with Potassium tert-Heptoxide
(29) .................................... ...... 82

Sodium Bis(trimethylsilyl)amide (30)............. 83

Preparation and Titration of a Solution of
Sodium Bis(trimethylsilyl)amide (30) in
Benzene. ..................................... 83

Treatment of 12a with Sodium Bis(trimethyl-
silyl)amide (30) in Liquid Sulfur Dioxide.... 84

Treatment of 12a with Sodium Bis(trimethyl-
silyl)amide (30) in Various Solvents at
25"C. Purification of l-tert-Butyl-2,2-
diphenylaziridine (22) ....................... 85

Authentic l-tert-Butylamino-2,2-diphenyl-
ethylene (31) ................................. 87

Treatment of l-tert-Butyl-2,2-diphenyl-
aziridine (22) with Florisil. 1-tert-
Butylamino-2,2-diphenylethylene (31)......... 88

Treatment of l-tert-Butyl-2,2-diphenyl-
aziridine (22) with Aqueous Perchloric
Acid. 1,l-Diphenyl-2-tert-butylamino-
ethanol (32).................................. 88

Attempted Trapping of the Supposed Ylide 42
with Norbornene (43) ......................... 89

Treatment of N-(Benzhydrylidene)dimethyl-
aminium Fluorosulfonate (12b) with the
Silylamide Base (30)........................ 89









CHAPTER III EXPERIMENTAL (Continued) Page

Treatment of N-(Benzhydrylidene)methyl-
allylaminium Fluorosulfonate (12c) with
the Silylamide Base (30) ..................... 90

Treatment of N-(Benzhydrylidene)methyl-
benzhydrylaminium Fluorosulfonate (12d)
with the Silylamide Base (30)................. 91

Treatment of N-(Benzhydrylidene)methyl-
anilinium Fluorosulfonate (12e) with the
Silylamide Base (30) ......................... 92

General Procedure for the Preparation of the
Aldimines (10) ............................... 93

N-(Benzylidene)tert-butylamine (10a)............. 93

N-(Benzylidene)methylamine (10b)................. 93

N-(Benzylidene)allylamine (10c).................. 94

N-(Benzylidene)benzylamine (10d)................. 94

N-(Benzylidene)aniline (10e)..................... 95

General Procedure for the Preparation of the
Aldiminium Salts (14) ........................ 95

N-(Benzylidene)methyl-tert-butylaminium
Fluorosulfonate (14a) ........................ 95

N-(Benzylidene)dimethylaminium Fluorosulfonate
(14b)........................................ 96

N-(Benzylidene)methylallylaminium Fluoro-
sulfonate (14c) .............................. 97

N-(Benzylidene)methylbenzylaminium Fluoro-
sulfonate (14d)............................... 97

N-(Benzylidene)methylanilinium Fluoro-
sulfonate (14e) .............................. 98

Authentic N-Methyl-N-tert-butylbenzamide (47)... 98

Decomposition of N-(Benzylidene)methyl-tert-
butylaminium Fluorosulfonate (14a) with
Aqueous Base, and Derivatization of Product
46. N-Methyl-N-tert-butylbenzamide (47)..... 99

Authentic l-tert-Butyl-2-phenylaziridine (39)... 100


viii









CHAPTER III EXPERIMENTAL (Continued)


Treatment of N-(Benzylidene)methyl-tert-
butylaminium Fluorosulfonate (14a) with
Potassium tert-Butoxide (28). Isolation
and Purification of Aminoether 48............ 100

Decomposition of Aminoether 48 with Deu-
terium Oxide................................. 101

Decomposition of Aminoether 48 with Aqueous
Base, and Derivatization of Product 46.
N-Methyl-N-tert-butylbenzamide (47).......... 101

Treatment of N-(Benzylidene)methyl-tert-
butylaminium Fluorosulfonate (14a) with
Sodium Bis(trimethylsilyl)amide (30).
Isolation and Purification of Diamino-
stilbene 52 and the Major and Minor
Aminomethylaziridine Isomers (50) ............ 102

Pyrolyses of the Major and Minor Isomers of
Aminomethylaziridine (50) .................... 105

Attempted Trapping with Norbornene (43) ......... 106

Stability of l-tert-Butyl-2-phenylaziridine
(39) to the Deprotonation Conditions......... 106

Stability of the Major Isomer of Amino-
methylaziridine 50 to Sodium Bis(tri-
methylsilyl)amide (30) ....................... 107

Authentic a,a'-Bis(dimethylamino)stilbene
Isomers (53) ................................. 108

Treatment of N-(Benzylidene)dimethylaminium
Fluorosulfonate (14b) with the Silylamide
Base (30) .................................... 108

Treatment of N-(Benzylidene)methylallyl-
aminium Fluorosulfonate (14c) with the
Silylamide Base (30) ......................... 109

Treatment of N-(Benzylidene)methylbenzyl-
aminium Fluorosulfonate (14d) with the
Silylamide Base (30) ......................... 110

Treatment of N-(Benzylidene)methylanilinium
Fluorosulfonate (14e) with the Silylamide
Base (30) .................................... 111

N-Methylbenzanilide (101) ....................... 111



ix


Page









CHAPTER III EXPERIMENTAL (Continued)


N- (a-Ethoxybenzylidene)methylanilinium
Triflate (98) ................................ 112

Authentic N-Phenylbenzimidoyl Chloride (103).... 113

Treatment of N-Methylbenzanilide (101) with
Thionyl Chloride. N-Phenylbenzimidoyl
Chloride (103) ............................... 114

N-(a-Chlorobenzylidene)methylanilinium Fluoro-
sulfonate (99) ............................... 114

Treatment of N-(a-Ethoxybenzylidene)methyl-
anilinium Triflate (98) with Potassium
tert-Butoxide (28) ........................... 115

Treatment of N-(a-Ethoxybenzylidene)methyl-
anilinium Triflate (98) with Sodium Bis-
(trimethylsilyl)amide (30) ................... 115

Treatment of N-(a-Chlorobenzylidene)methyl-
anilinium Fluorosulfonate (99)with Sodium
Bis(trimethylsilyl)amide (30) ................ 116

2-Phenyl-l-azirine (100a) ....................... 117

2,3-Diphenyl-l-azirine (100b) ................... 117

2-Phenyl-3-carbethoxy-l-azirine (100c) .......... 118

Treatment of 2-Phenyl-l-azirine (100a) with
Methyl Triflate (llb) ........................ 118

Treatment of 2,3-Diphenyl-l-azirine (100b)
with Methyl Triflate (11b). 2-H-3,4,6,7-
Tetraphenyl-2,5-diaza-2,4,6-heptatrienium
Triflate (109) ............................... 119

Treatment of 2-H-3,4,6,7-Tetraphenyl-2,5-
diaza-2,4,6-heptatrienium Triflate (109)
with Aqueous Base. 3,4,6,7-Tetraphenyl-
2,5-diaza-2,4,6-heptatriene (110) ............ 121

Treatment of 3,4,6,7-Tetraphenyl-2,5-diaza-
2,4,6-heptatriene (110) with Trifluoro-
methanesulfonic Acid. 2-H-3,4,6,7-Tetra-
phenyl-2,5-diaza-2,4,6-heptatrienium
Triflate (109) ............................... 122

Authentic N-Methyltetraphenylpyrazinium
Triflate (111) ............................... 123


Page








CHAPTER III EXPERIMENTAL (Continued)

Treatment of 2-H-3,4,6,7-Tetraphenyl-2,5-
diaza-2,4,6-heptatrienium Triflate
(109) with Aqueous-Ethanolic Acid. N-
Methyltetraphenylpyrazinium Triflate
(111)........................................

Treatment of 2-Phenyl-3-carbethoxy-l-
azirine (100c) with Methyl Triflate (llb)....

REFERENCES...............................................

NMR SPECTRA...............................................

NMR
SPECTRUM


Page





123


124

126

131


1. N-(Benzhydrylidene)methyl-tert-butyl-
aminium Fluorosulfonate (12a) in SO2..... 132

2. N-(Benzhydrylidene)dimethylaminium Fluoro-
sulfonate (12b) in SO ................... 133

3. N-(Benzhydrylidene)methylallylaminium
Fluorosulfonate (12c) in SO2............. 134

4. N-(Benzhydrylidene)methylbenzhydrylaminium
Fluorosulfonate (12d) in DMSO-d6......... 135

5. N-(Benzhydrylidene)methylanilinium Fluoro-
sulfonate (12e) in SO2................... 136

6. N-(Benzhydrylidene)tert-butyliminium
Triflate (20) in DMSO-d6................. 137

7. N-(Benzylidene)methyl-tert-butylaminium
Fluorosulfonate (14a) in SO2............. 138

8. N-(Benzylidene)dimethylaminium Fluoro-
sulfonate (14b) in SO2................... 139

9. Isomers of N-(Benzylidene)methylallyl-
aminium Fluorosulfonate (14c) in SO2..... 140

10. Isomers of N-(Benzylidene)methylanilinium
Fluorosulfonate (14e) in SO2............. 141

11. Mixture (in CC14) Obtained from the Re-
action of 12a with Potassium tert-
Butoxide in Ether........................ 142

12. l-tert-Butyl-2,2-diphenylaziridine (22)
in CC14... .............................. 143








NMR SPECTRA (Continued) Page

13. l-tert-Butylamino-2,2-diphenylethylene
(31) in CC14 ............................. 144

14. N-Methyl-N-tert-butylbenzamide (47) in
CC1 .......................... ......... 145

15. Aminoether 48 in CC14....................... 146

16. Major Isomer of Aminomethylaziridine 50
(major-50) in CC14..................... . 147

17. Minor Isomer of Aminomethylaziridine 50
(minor-50) in CC14................. ..... 148

18. Isomers of a,a'-Bis(dimethylamino)stil-
bene (53) in CC14...................... 149

19. a,a'-Bis(methyl-tert-butylamino)stilbene
(52) in CC14... ....................... 150

20. Isomers of N-(a-Ethoxybenzylidene)methyl-
anilinium Triflate (98) in SO ........... 151

21. N-(a-Chlorobenzylidene)methylanilinium
Fluorosulfonate (99) in DMSO-d6.......... 152

22. 2-H-3,4,6,7-Tetraphenyl-2,5-diaza-2,4,6-
heptatrienium Triflate (109) in SO2 ...... 153

23. 3,4,6,7-Tetraphenyl-2,5-diaza-2,4,6-
heptatriene (110) in SO............... 154

24. N-Methyltetraphenylpyrazinium Triflate
(111) in SO2 .............................. 155

BIOGRAPHICAL SKETCH ................................... 156















LIST OF TABLES


Table Page

I. Ketimines and Ketiminium Salts................... 9

II. Aziridine:Imine (22:9a) Distribution Obtained
from the Reaction of [Ph2C=N(Me)t-Bu](OSO2F)
(12a) with Various Base-Solvent Combinations..13

III. Aldimines and Aldiminium Salts...................21

IV. Nmr Spectral Assignments for the Diastereo-
isomers of Compound 50........................26

V. Material Balance and Product Distribution Ob-
tained from the Reaction of [Ph2C=N(Me)t-Bu]
(OS02F) (12a) with NaN(SiMe3)2 (30) in
Various Solvents at 25C ......................86


xiii















Abstract of Dissertation Presented to the
Graduate Council of the University of Florida in
Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy



DEPROTONATIONS OF TERNARY IMINIUM SALTS

By

William Anthony Szabo

December, 1974



Chairman: James A. Deyrup
Major Department: Chemistry



The deprotonation of ternary iminium salts as a method

for synthesizing aziridines via azomethine ylides was in-

vestigated. The salts were prepared by alkylating ketimines

and aldimines with methyl fluorosulfonate. A variety of

strong bases (but poor nucleophiles) were studied as

potential deprotonating agents. In one case, the ketiminium

salt N-(benzhydrylidene)methyl-tert-butylaninium fluoro-

sulfonate was converted to l-tert-butyl-2,2-diphenylaziridine

in excellent yield, upon treatment with the base sodium

bis(trimethylsilyl)amide in hexane.

Different results were obtained with the structurally

related aldiminium salt N-(benzylidene)methyl-tert-butyl-

aminium fluorosulfonate, under the same reaction conditions.








The expected l-tert-butyl-2-phenylaziridine was not

detected in the crude product mixture. Instead, the

isolated and characterized products were a,a'-bis(methyl-

tert-butylamino)stilbene, and two aminomethylaziridine

diastereoisomers. Mechanisms that are consistent with

these observations are discussed.

Two approaches to the synthesis of the unknown,

potentially antiaromatic 2-azirine system were tested.

The first approach involved the treatment of certain

heterosubstituted iminium salts with a strong base, in

an effort to generate aziridines which could be transformed

in situ to 2-azirines. The second approach was the

attempted alkylation and subsequent deprotonation of the

known 1-azirine isomers. The major product of the treatment

of 2,3-diphenyl-l-azirine with methyl triflate was the

novel, alkylated dimer 2-H-3,4,6,7-tetraphenyl-2,5-diaza-

2,4,6-heptatrienium triflate. However, neither approach

provided evidence for the formation of the 2-azirine system.















CHAPTER I

APPLICATIONS TO THE SYNTHESIS OF AZIRIDINES



Introduction

The reversible thermal ring openings of aziridines

(1) to resonance-stabilized azomethine ylides (2) are

well-known reactions. '2 The classical trapping ex-

periments of Huisgen, for example, have provided con-

vincing tests of the Woodward-Hoffmann rules of orbital










1. 2


symmetry, and have contributed significantly to the area

of 1,3-dipolar cycloadditions.

In spite of their impact on mechanistic organic

chemistry, these thermolytic reactions are of little

synthetic use for the preparation of aziridines. It was

the plan of this research to generate 1,3-dipolar inter-

mediates from non-aziridine precursors, thereby rendering

this a practical method for the synthesis of aziridines.

Although azomethine ylides have been generated from








several non-aziridine precursors,4 the ternary iminium

salts of type 3 seemed to offer the most general route

to functionally substituted 1,3-dipoles: deprotonation

of 3 with a suitable base would afford the desired


H

+ base A7
N -HX N

X

3 I


intermediate 2 which, it was hoped, would cyclize to the

aziridine, as shown in equation 2. The choice of which

iminium salts to use was subject to several structural

constraints: (1) the salt had to bear substituents

which would, both electronically and sterically, encourage

intramolecular cyclization of the incipient ylide; (2) the

substituents on the a-carbon atom of 3 had to be devoid of

protons, to preclude enamine formation upon treatment with

base; and (3) the anion X had to be sufficiently non-

nucleophilic that it did not interfere with the reaction

chemically.

In principle, one could encourage intramolecular

isomerization of 2 by utilizing very reactive azomethine

ylides, whose lifetime was sufficiently short that inter-

molecular reaction was not a competing process. The

reactivity of azomethine ylides, in turn, is a function

of both electronic and steric factors. Huisgen has shown,








for example, that electron-withdrawing groups attached

to the dipolar termini decrease the reactivity of the

ylides, relative to the effect of electron-donating

substituents. These electronic effects on dipolar

reactivity are reflected in the temperatures that are

required to effect the ring opening (equation 1) of

different aziridines: the higher the temperature, the

more reactive the resulting azomethine ylide. Thus,

whereas 2,3-dicarbethoxyaziridines cleave at 100C,la

the corresponding 2,3-diphenyl derivatives require re-

fluxing in toluene for 11 hours.2a

Steric factors also influence the tendency of 1,3-

dipoles to undergo intramolecular cyclization. When relief

of strain accompanies the ring opening of certain bicyclic

aziridines, for example 42b and 5,2e the resulting azo-

methine ylides are found to be particularly stable to the

reverse process of ring closure. This effect is also





H H

Ph A PAr

N NH NA N N+
OQ/N&Ar
Me Me


4 5 6


Ar = p-nitrophenyl








partially responsible for the total reluctance of the
4a
first reported azomethine ylide, 6, to isomerize to

the corresponding aziridine. The stability of 6 (and

of the ylides derived from 4 and 5) is further enhanced

by the electron-withdrawing effect of the a-nitrophenyl

substituent, as discussed above. In addition to these

effects, it has been found that azomethine ylides that

are sterically incapable of the symmetry-allowed3 conro-

tatory ring closure are thermally stable to intramolecular

cyclization. Conversely, the aziridine precursors to

such ylides (e.g., 71d and 82c) are very resistant to

thermolytic cleavage, since a concerted ring opening

0 0
,H ,H
-Me-N N-R R-N N-CH2Ph
'H 'H
0 0
7 8

R =p-anisyl

would require the same difficult conrotatory motion.

Finally, it might be expected that the steric demands

of substituents on the nitrogen atom of the azomethine

ylide should affect the propensity for intramolecular



*
Since the azomethine ylides are isoelectronic with
the allyl anion, and since the highest occupied molecular
orbital of the latter has a node at the central atom,
it has been suggested (reference 5a) that small differences
in the electronic characteristics of substituents on the
nitrogen atom of the ylides should have little effect on
the frontier-orbital energies of their dipolar termini.








cyclization. It can be argued, for example, that bulky

substituents that encounter severe steric interactions

with functional groups on either (or both) of the dipolar

termini should force the termini together, resulting in

a more facile closure to the aziridine. Indeed, it has

been postulated5 that even linear 1,3-dipoles (e.g.,

nitrile ylides) are bent in their transition states for

cycloaddition reactions, ostensibly so that p-orbital over-

lap of the dipolar termini with the appropriate orbitals of

the dipolarophile is maximized.

In view of the above considerations, ternary iminium

salts of type 12-15 were reasoned to be likely precursors

of azomethine ylides which would undergo the facile valence-

bond isomerization to form aziridines. The reactivity of

the derived 1,3-dipoles should be assured by the phenyl-

substituted terminus and, perhaps, by bulky substituents

(R' in equation 3) on the nitrogen atom. The problem of

enamine formation videe supra) would be obviated. The

ketiminium salts 12 and 13 and the aldiminium salts 14

and 15 offered the potential to observe any substituent


Ph Ph
XSO2OMe

NR' R., X = F R N(Me)R' (3)
R b, X=CF3 R
-OSO2X

9, R=Ph 12, R=Phi X=F

10, R = H I3, R=Phi X=CF
14, R= H; X = F
15, R= H, X= CF3








effects on the outcome of the deprotonation reactions.

Finally, the fluorosulfonate and trifluoromethanesulfonate

(or "triflate") anions were chosen because of their

extremely low nucleophilicities. These anions could be
incorporated into the iminium salts by alkylating imines

9 and 10 with methyl fluorosulfonate (lla)7 or methyl

triflate (llb). These powerful alkylating agents are
available commercially, and the imine precursors are

readily accessible.

The problem that remained, then, was one of selecting

a base which was suitably non-nucleophilic that other re-

actions did not compete with the desired deprotonation

(path 1 in Scheme I). For example, the base could act via



Scheme I


Ph H~

+ CH base


R =



R = Ph, H


Ph Ph
path I R CH 2
SR' R

L J IR
R


path 2


Ph

^N:
R I
R


Ph
path 3 R-L4 Me


-----. ETC.








path 2 to produce the dealkylated imine, or it might add

to the electrophilic iminium salt (path 3) to produce

adduct 16, which could react further under the reaction

conditions. With the recent availability of strong,
9
proton-specific bases, the experimental problem at this

point would be one of finding the most efficient base for

the purpose described.


Ketiminium Salts
Results

A variety of ketimines (9) were prepared by slight
10
modification of the method of Moretti and Torre, as

shown in equation 4. A solution of benzophenone in

dichloromethane was stirred with a tenfold excess of the





TiCI4
Ph2C=O + R'NH2 Ph2C=NR' (4)
CHg2CIg

9




XS020Me +
Ph2C=NR' solvent Ph2C=N(Me)R' (5)
solvent

9 "OS02X
9 X = F, CF3 O02

12, = F

3, X = CF3









appropriate primary amines, in the presence of titanium

tetrachloride. As shown in Table I, the products were

isolated in about 65-95% yield. Alkylation of the ketimines

with methyl fluorosulfonate and methyl triflate afforded

the corresponding N-methyl ketiminium salts 12 and 13,

respectively. The results of the alkylation experiments

are also presented in Table I. For example, the repre-

sentative compound 12a is a white solid that can be

recrystallized from absolute ethanol. Although it is

slowly decomposed by atmospheric moisture over a period of

several days, it can be stored in a drybox for several

months without appreciable decomposition. This salt is

relatively insoluble in hexane, carbon tetrachloride, ben-

zene, ether, and chloroform. It is readily soluble, however,

in polar solvents such as hexamethylphosphoramide (HMPA),

acetone, dimethyl sulfoxide (DMSO), and liquid sulfur

dioxide. Its nmr spectrum, taken in the latter solvent,

shows a methyl resonance (63.86) which is deshielded by

43 Hz with respect to that of N-(benzhydrylidene)methylamine

(9b). This downfield shift can be attributed to the in-

ductive effect of the positively charged nitrogen atom of

12a on the methyl protons. Olah and Kreienbuhl11 have re-

ported similar chemical shifts for related, protonated

ketimines.

Interestingly, the triflate salt 13a decomposes at

128 with the liberation of a gas, presumably isobutene,

as shown in equation 6. The crystalline residue was assigned



















ez H
H






0 r-l









II d w
E a) \t0










,0 .0




0




-H 4

II


















0
U
z a

N







a



P4a0
E- -
0)c
Ur -


H- I N M p L


r- o o
m1 0 0
H r-









r-1 ra +


0,0




U


m t.







tOH
.4J C 4-)
a) U a)
C12
000a


M om M H







'I | 0 | 0I 0'.I 0 I









0 0 rH C1
SmB a >, -
4Pl -PJI Hl a
3d U








structure 17, based on the deshielded methyl singlet
(63.47) in its nmr spectrum, and the conspicuous absence


Ph
l + ,Me
Ph

t-Bu

OS 02CF3
13a


Ph

1280 Me
4H Ph
-C4H8 I


-OS02CF3

17


of a tert-butyl resonance.
A limit to the success of the alkylation procedure
is indicated by two other experiments. Whereas alkylation
of 18a with methyl fluorosulfonate proceeds within ten
minutes to afford the expected product (19a) in 92% yield,
attempts to methylate the corresponding tert-butyl deriva-


FSO2OMe
CHCl3
0, N2


18a, R = Me
b, R = t-Bu


OSO2F
19a, R=R'=Me
b, R=t-Bu; R'=H


tive (18b) under the same reaction conditions resulted only
in the isolation of 19b, in 6% of the theoretical yield
(based on 18b). More 19b was recovered after storing the
reaction filtrate in a refrigerator overnight. Similarly,







whereas ketimine 9a is readily alkylated with methyl

triflate, treatment with ethyl triflate affords only the
protonated salt 20 (NMR SPECTRUM 6), as shown in Scheme
II. The yield of 20 after 48 hours, however, was only 18%.


Scheme II


Ph Ph Ph
L CF3SO2OEt +.H 1900 +
Ph N H N h NH2
Ph CHCI3 Ph -C4H8 Ph 2
t-Bu 00,N2 t-Bu
OS02CF3
OS OgCF3
9a 2 21
20 -
T -


10% No OH


Compound 20 suffered loss of isobutene on pyrolysis, to
produce the primary iminium salt 21 in quantitative yield.

In addition, 20 was readily deprotonated by aqueous sodium
hydroxide to return the parent ketimine 9a. It seems un-
likely that these protonations occur by an alkylation-
elimination process, because it is difficult to explain
why the lower-alkyl substituents should be eliminated in


*
In related cases, recall that the classical Decker
amine synthesis (reference 12) fails when imine alkylation
is attempted with substituents larger than methyl; also,
Ford (reference 13) has recently reported the resistance of
two highly hindered amines to alkylation with fluorosul-
fonates larger than the methyl ester.








preference to the tert-butyl group. It is more probable

that large steric demands by substituents on either terminus

of the C=N (e.g., the necessarily planar fluorene moiety and

the N-tert-butyl group) seriously inhibit alkylation, and

that the proton source is the acid which is slowly produced

when traces of moisture in the system hydrolyze the alkyl-

ating agents.

With the availability of the ketiminium salts listed

in Table I, the problem of deprotonation was confronted.

Using 12a as a model compound, it was found that treatment

with a variety of bases did, in fact, produce the desired

aziridine, compound 22. Inevitably, however, 22 was con-

taminated with varying amounts of the nucleophilically dis-

placed product 9a and benzophenone, as indicated in equation


Ph
Ph Ph
P +-Me bose Ph L
Ph solvent Ph N Ph N Ph
t-Bu I t-Bu
t-Bu

OSO2F 2 9a

12a (8)


8. The experimental conditions and the results of various

deprotonations are summarized in Table II. These reactions

were performed by adding the appropriate solvent to a

stirring mixture of the iminium salt and a slight molar

excess of the base, at various temperatures. The lithium









Table II. Aziridine:Imine (22:9a) Distribution Obtained
from the Reaction of [Ph2C=N(Me)t-Bu](OSO2F) (12a) with
Various Base-Solvent Combinations


a b
Base Compd Ref Solvent(s) T 22:9a-


n-BuLi


ether-
hexane


Me2N NMe2






Me2 Me2
N
Li


OLi
t-Bu t-Bu




NaCH2S(O)Me

KO-t-Bu



KOCEt3

NaN(SiMe3)2


20 ether







9a ether-
hexane


ether-
hexane


60 DMSOe
61 HMPA
61 HMPA-


ether


62 xylene

14 SO2

DMSO'

ether


c
25 0-


-78 (n.r.)







25 -0.7



d
-78 1-


25 2

0 0.4

-78 13

25 13

-78 0


benzene

hexane


-Initial reaction temperature, C. -Mole-%,dby nmr
spectral assay. LLittle, if any, 22 detected. -Recovered
70% of the iminium salt. eHomogeneous mixture.








bases 25 and 26 were prepared in situ from commercial n-

butyllithium (23) in hexane. All deprotonations were

carried out in an atmosphere of dry nitrogen. Almost

invariably, a transient, deep red color was observed as

the solvent was added to the salt-base mixture. The system

was stirred at room temperature for one hour, and was then

filtered. The filtrate was concentrated in vacuo, and the

residue was assayed by careful integration of its nmr

spectrum (for an example, see NMR SPECTRUM 11).

It is evident from the data in Table II that the most

efficient base investigated in this study was sodium bis-

(trimethylsilyl)amide, compound 30. This base is conven-

iently prepared in 85-95% yield by refluxing the inexpensive,

commercially available hexamethyldisilazane with sodium

amide in benzene, according to the method of Kruger and

Niederprum.14 The base is soluble in a variety of organic

solvents (e.g., ether, benzene, xylene, HMPA, and DMSO). It

was found that solutions of 30 in benzene could be readily

assayed by titrating the sodium hydroxide that remained when

the solutions were decomposed with boiling water:


NaN(SiMe3)2 3H20 2Me3SiOH(g) + NH3(g) + NaOH (9)
30


Considering the very high material balance and favorable

product distribution which resulted when base 30 was used

in hexane, l-tert-butyl-2,2-diphenylaziridine (22) was

synthesized in almost quantitative yield.








Aziridine 22 was identified by its spectral properties

(see, for example, NMR SPECTRUM 12), and by the degradation

experiments outlined in Scheme III. Passage of 22 through

a column of Florisil afforded a mixture of the enamine 31


Scheme III

Ph Ph Ph

Ph- 7 Florisil P H N r H
P N Ph"Y HI/

t-Bu -Bu


I-BuNH2
HC104 H20 Florisil -H20


PhP C(OH)CH N(H)t-Bu -- Ph CHCHO --


32


33


.(NMR SPECTRUM 13) and its hydrolysis product, diphenylacetal-

dehyde (33). The structure of 31 was confirmed by synthesis

from authentic 33 and tert-butylamine. The isomerization

of 22 to 31 has precedent in the chemical literature,1 as

does the formation of alcohol 32 from 22.1

Disappointingly, none of the other ketiminium salts

listed in Table I produced clean reactions upon treatment

with sodium bis(trimethylsilyl)amide in benzene, although

the reactions were invariably accompanied by intense color
changes. For example, the physical characteristics and nmr








spectra of the crude mixtures obtained from ketiminium

salts 12b and 12c indicated that gross polymerization had

taken place. Benzophenone was the major product of the

attempted deprotonation of the benzhydryl analog 12d.

The nmr spectrum of the crude product mixture showed a

singlet of low intensity at 62.32, possibly due to one of

the compounds 34, 35, or 36. The mixture was not character-

ized further. The methylanilinium fluorosulfonate 12e

Ph Ph Ph


Ph N Ph Ph Ph2CHNHCH3

I I
CH3 CHPh2
36

34 35


afforded a product mixture whose nmr spectrum indicated

the presence of N-(benzhydrylidene)aniline (9e), N-methyl-

aniline, and benzophenone. In addition, it is likely that

a prominent singlet at 62.77 belonged to the methylene

protons of the expected (but unreported) aziridine 41:

consider the deshielding effect of geminal diphenyl sub-

stitution on the chemical shifts of the indicated protons
17)
of compound 37 (60.9317) versus 38 (62.1218), and 39

(61.4416) versus 22 (62.16). By analogy, it is not unrea-

sonable to expect that the methylene protons of compound 41

would resonate at least 0.4 ppm downfield from the indicated
proton of compound 40 (2.3419). Unfortunately, all attempts
proton of compound 40 (62.34 ). Unfortunately, all attempts










Ph H Ph H Ph H


R H R V H RA H

I I I
H t-Bu Ph


37, R =H 39, R =H 40, R=H

38, R = Ph 22, R = Ph 41, R = Ph


to isolate the supposed aziridine 41 by column chromato-

graphy, distillation, fractional crystallization at -78,

and perchlorate extraction were fruitless. Somewhat sur-

prisingly, the latter technique returned N-methylaniline

as the only extractable basic product.
Discussion

It is difficult to discern trends in the product ratios

listed in Table II as a function of the bases and solvents

used. It appears that the necessary conditions for the

high conversion of 12a to aziridine 22 are the use of a

strong, hindered base under heterogeneous, anhydrous con-

ditions.
20
Thus, whereas 1,8-bis(dimethylamino)naphthalene (24)2
is a hindered base, it is a relatively weak one (pK_ 12.3420).

Whereas n-butyllithium (23) is a very strong base, it is

probably not hindered enough to be selective. Furthermore,

it is known21 that the thermal and photochemical generation

of certain azomethine ylides from aziridines is highly








solvent dependent. In the present study, it appears that

nonpolar solvents and heterogeneous reaction conditions

gave the best results. An alternative to this solvent-

effect explanation is the possibility that rigorous ex-

clusion of moisture is necessary for favorable product

distributions. Although traces of moisture in the mixture

were shown to have little direct effect on the integrity

of the ketiminium salt, the bases used in this study are

extremely susceptible to hydrolysis. The products of

hydrolysis (alkali-metal hydroxides) might then be re-

sponsible for less-favorable product ratios, as well as

for the production of benzophenone. Evidence for this

possibility was the observation that the hygroscopic sol-

vents, ether and DMSO, produced lower yields of the aziri-

dine using the silylamide base than did the hydrophobic

solvent, hexane. In addition, the reaction in hexane

produced only a very small quantity of benzophenone.

Although it is tempting (and not unreasonable21) to

speculate that the transient color observed in the depro-

tonation of 12a was due to the azomethine ylide 42, there

was no direct evidence that this was the case. Attempts

to trap 42 with conventional dipolarophiles (equation 10)

were unsuccessful. A major experimental problem was the

instability of most of the trapping agents tried (e.g.,

dimethylacetylenedicarboxylate, benzaldehyde, and acetone)

to the strong bases. Norbornene (43), on the other hand,

failed to react with anything under the reaction conditions










Ph Ph a-b


Ph Ph 2 Ph
IH I I a-
t-Bu t-Bu t-Bu


42
(10)



of 12a and NaN(SiMe3)2 in benzene at 250. Of course, as
Padwa and Hamilton have demonstrated,21 failure to trap
the postulated ylide does not nullify the possibility of
its intermediacy. Rather, this result may simply be

H H H H





Ph
H H
43 44


attributed to the low steady-state concentration of a highly
reactive species. Alternatively, it is known that steric
factors can affect the ratesld and regioselectivities2i,5b
of dipolar cycloadditions. It can easily be appreciated
by inspection of geometry 44 that the most probablele
transition state for the cycloaddition of 42 to norbornene
might be sufficiently crowded that this reaction can not








compete effectively with intramolecular closure of the

azomethine ylide.

Based on the experimental data which are available, it

is not possible to explain the different results that were

obtained for the tert-butyl ketiminium salt vis-a-vis the

other derivatives. The complexities associated with two-

phase reactions, and the fact that reaction conditions

were not optimized for salts other than 12a, make any such

rationalizations purely speculative.


Aldiminium Salts

Results

It was found that aldimines (10) could also be pre-

pared and smoothly alkylated with methyl fluorosulfonate,



PhCHO + R'NH2 PhCH=NR' (II)
-H20
10


FSO2OMe +
PhCH=NR' PhCH=N(Me)R' (12)
ether

10 -780, N2 OS2F

14


to afford the corresponding aldiminium salts 14 in high

yield (equations 11 and 12), as summarized in Table III.

The alkylations were effected in ether at low temperature,

and the crude products were isolated as white solids having








Table III. Aldimines and Aldiminium Salts


PhCH=NR' [PhCH=N(Me)R'] (OSO2F)

Yield Yield NMR
R' Compd (%) Compd (%) SPECTRUM


t-Bu 10a 95 14a 99 7

Me 10b 95 14b 96 8

allyl 10c 79 14c 99 9

CH Ph 10d 100 14d -

Ph 10e 84 14e 98 10


broad melting ranges. An exception was 14d, which was

isolated as an oil. Unlike the ketiminium salts, the

alkylated aldimines are very hygroscopic, and had to be

synthesized and manipulated in a nitrogen-purged drybox.

The nmr spectra of several of the aldiminium salts,

taken in liquid sulfur dioxide, clearly indicate a mixture

of entgegen and zusammen isomers. For example, NMR SPECTRUM

10 of compound 14e shows a 4:1 mixture, with the upfield

methyl resonance belonging to the major isomer. From

steric considerations alone, one would predict the major

isomer to be 45a, with its more favorable disposition of

aromatic rings, relative to 45b. Indeed, NMR SPECTRUM 7

of the tert-butyl derivative (14a) indicates almost exclu-

sively a single isomer, presumably also the entgegen isomer.

In addition, the slightly higher chemical shift of the

methyl doublet belonging to the major isomer of 45 can be

attributed to shielding by the proximate C-phenyl substituent








Ph


H N
I
Ph


45a


Ph
H Ph

I
CH3


45b


of isomer 45a. Keenan and Leonard22 have made the same
assignment for the methyl substituents of a closely
related iminium salt.
As chemical proof of the structure of these salts,
compound 14a was subjected to basic hydrolysis as shown
in Scheme IV, and the resulting amine was scavenged with

Scheme IV


t-BuNC


Ph

IMe

t-Bu
OSO2F

14a


10% NaOH


Li AIH4


HN(Me)t-Bu + PhCHO
46


10% NaOH PhCOCI


PhCON(Me)t-Bu








benzoyl chloride. The product was amide 47 (NMR SPECTRUM

14). The same amide was produced by similar derivatization
of authentic methyl-tert-butylamine (46), prepared by
reducing tert-butyl isocyanide with lithium aluminum
hydride.23
The results of the attempted deprotonation of 14a

with a slight excess of potassium tert-butoxide in ether
are shown in Scheme V. It was demonstrated that the

expected aziridine 39 was not a component of the crude
reaction mixture, by comparing the tlc behavior and spec-
tral properties of the mixture with those of authentic16
39. Instead, 80% of the crude reaction product consisted
of the aminoether 48, accompanied by the demethylated


Scheme V


KO-i-Bu
ether
-780


t-Bu
Ph Ph
H N"Me N
0 tB H + PhCHO
-t-Bu

4810a

I D20
DzOg


PhCHO + t-BuOD + DN(Me)t-Bu

49


PhCOCI
4710% N
10% NaOH


Ph
,L Me
H ^N
t-Bu
OS02F
14a




Ph

H N7
N
t-Bu
39








product 10a (12%) and benzaldehyde (5%). Compound 48,

formally derived from the direct addition of tert-butoxide

to the aldiminium salt, was purified by distillation and

identified by its spectral properties (see, for example, NMR

SPECTRUM 15). In addition, a facile deuterolysis converted

48 to equimolar quantities of benzaldehyde, deuterio-tert-

butanol, and amine 49 (Scheme V). The latter compound was

characterized as its benzamide derivative, 47.

Treatment of the aldiminium salts 14a and 14b with

sodium bis(trimethylsilyl)amide in benzene produced the


Ph

+ Me
H N
I
R "OSO2F

14a, R = t-Bu
b, R =Me


No N(SiMe3)2
benzene
r.t., N2


Ph I
H'-V Me

Ph
N
I
R
50, R = t-Bu
51, R= Me


R
Ph I
"Y.N Me

C(Ph)N-Me


52, R t-Bu
53, R Me


The dimers 50 and 52 videe infra) were also produced
in this reaction, to the combined extent of 3% of the prod-
uct mixture.








unexpected results indicated by equation 13. Again, aziri-

dine 39 was conspicuously absent from the product mixture.

The structure of product 50 was assigned on the basis of

spectral and chemical evidence. It was possible, for

example, to isolate both diastereoisomers of 50 by careful

silica gel chromatography of the crude product mixture.

The major and minor isomers (5:1 in the crude mixture)

were assigned the relative configurations 50a and 50b,

respectively. The structures are drawn in their most

probable conformations, from consideration of molecular

models. The assignments are based on the nmr data given

in Table IV (from NMR SPECTRUM 16 of the major isomer and

NMR SPECTRUM 17 of the minor isomer), and the arguments

which follow:

(1) The prochiral Ht protons of the two isomers are

in similar stereochemical environments and, therefore,

should have similar chemical shifts. In the absence of

a suitable model compound, one can not say with certainty

which of the two doublets in the spectrum of the major

isomer belongs to Ht, due to their similar chemical shifts.

However, one can assign the downfield doublet of the minor

isomer to Ht, because its chemical shift (61.68) is closest

to that of Ht of the major isomer (61.74 or 61.98). The




The possibility that the isomers are conformational
(rotational) diastereoisomers has not been excluded. How-
ever, the high barrier to rotation that would be necessary
to enable isolation of such isomers seems unlikely.











t-Bu




-- H" t-Bu


MAJOR ISOMER

50a



Table IV. Nmr Spectral
isomers of Compound 50


MINOR ISOMER

50b



Assignments for the Diastereo-


Chemical Shift (6,CC14)
Assignment Major Isomer Minor Isomer


-C(CH3)3 0.71 and 0.89 0.77 and 0.83

-Ha 1.74 or 1.98 1.13

-Ht 1.98 or 1.74 1.68

N-CH3 2.33 2.78

Ph-CH 4.48 4.13

-C6H5 7.0 to 7.5 7.0 to 7.5


aHc is the hydrogen atom which is on the same face
of the plane defined by the aziridine ring as the amino-
methyl side chain. The other methylene proton, then, is
Ht.








upfield doublet (61.13), then, must belong to H of the

minor isomer. Compared to the other aziridine protons,

and to the indicated proton in model compound 39 (61.44),

H in the minor isomer is fairly shielded. Inspection of

conformation 50b suggests that this effect may be induced

by the aromatic ring on the aminomethyl side chain of the

proposed minor isomer.

(2) The same aromatic ring in 50b which shields H


Ph H t-Bu
Ph I

N CH3 Ph C N
S0 II -CH3
t-Bu t-Bu 0 CH


39 48 47


is oriented in such a way that it deshields the N-methyl

protons of the minor isomer. Note that these protons

(62.78) are, in fact, deshielded: cf. the methyl protons

of amine 48 (62.21, NMR SPECTRUM 15) and amide 47 (62.75,

NMR SPECTRUM 14).

(3) The shielding of the methine proton of the minor

isomer vis-a-vis the major isomer is probably the result

of the position of this proton with respect to the shielding

zone of the phenyl group on the aziridine ring, a feature

which is not present in 50a.

A more definitive assignment of relative configuration must

await X-ray analysis.








As chemical proof of structure, it was demonstrated

that both of the isomers of 50 could be converted to

diaminostilbene 52 videe infra) by thermolysis in a

sealed capillary at 250.

Although product 51 decomposed on several attempts

to purify it, its presence in the product mixture obtained

from iminium salt 14b was deduced by spectral analogy with

the major tert-butyl isomer, 50a.

In addition to 51, a mixture of E- and Z-diaminostil-

benes 53a and 53b (NMR SPECTRUM 18) was produced in the

reaction of 14b with sodium bis(trimethylsilyl)amide. The

structures of these isomers were confirmed by synthesis of

a mixture of the authentic compounds, according to the
24
method of Scheeren and van Helvoort.24 The synthesis,

shown in Scheme VI, produces approximately equal quantities




Scheme VI



PhCHO + HNMe2 + NaCN PhCHNMe2 NaH
CN




Ph NMe2 Ph NMe2


Me2N Ph Ph NMe2


53b


53a








of 53a and 53b, as does the deprotonation reaction of

iminium salt 14b. The complete separation of E- and

Z-isomers was not effected. However, the nmr spectra

of various chromatographic fractions revealed that the

singlets at 62.28 and 67.18 belong to one isomer, and

those at 62.69 and 66.88 belong to the other. If one

assumes that the canted aromatic rings shield the methyl

protons of only the entgegen isomer (the methyl protons

of the zusammen isomer are not within the shielding zone

of the aromatic substituents), the upfield methyl singlet

can be assigned to isomer 53a. The chemical shift of

this resonance corresponds almost exactly to that of the

methyl resonance of the single diaminostilbene (52) which

is produced from the tert-butyl aldiminium salt, 14a (see

NMR SPECTRUM 19). Compound 52, then, is also assigned

the entgegen configuration. Of course, this assignment

is reasonable on the basis of steric considerations, too.

Interestingly, although treatment of the aldiminium

salts 14a and 14b with NaN(SiMe3)2 produced analogous prod-

ucts, the product distribution was markedly different.

Whereas the tert-butyl derivative afforded about nine times

as much of the aminomethylaziridine isomers 50 as the

diaminostilbene 52, the crude product mixture obtained

from the dimethyl derivative contained approximately equal

proportions of 51 and 53.

Treatment of the three other aldiminium salts with

sodium bis(trimethylsilyl)amide in benzene produced complex








mixtures. Products corresponding to 50 and 52 could not

be isolated from the mixtures, if, in fact, they were

present. For example, the N-allyl salt (14c) yielded

a mixture which, after column chromatography under the

same conditions that enabled the separation of 52 and

the isomers of 50, afforded benzaldehyde as the only

identifiable product. Treatment of the N-benzyl derivative

14d with the silylamide base produced 10d and 54 in small

amounts. No other component of the crude reaction mixture

was identified. The structure of 54 was confirmed by



PhCH=NCH2Ph HN(Me)CH2Ph PhCH=NPh


IOd 54 IOe



isolation of the compound via perchloric acid extraction,

and comparison of the ir and nmr spectra of the product

with those of authentic methylbenzylamine.25 Note that

the course of this deprotonation may have been altered by

the relatively impure state of the starting material: 14d

was isolated as an oil, which could not be crystallized.

N-(Benzylidene)methylanilinium fluorosulfonate (14e) pro-

duced a dark, viscous syrup upon treatment with NaN(SiMe3 2.

The mixture was shown by nmr spectral analysis to contain

several silylated species and N-(benzylidene)aniline, 10e.

In addition, there were several unidentified singlets in

the spectrum in the region 2.6-2.9 ppm.








Discussion

A priori, formation of the reaction products obtained

by treating the aldiminium salts 14a and 14b with sodium

bis(trimethylsilyl)amide can be explained by at least

three mechanisms. According to the first, which will be

arbitrarily labeled Mechanism A (Scheme VII), abstraction

of an aldiminium methyl proton by the base, followed by

intramolecular cyclization of the resulting azomethine


Scheme VII


MECHANISM A


4NCH2 base
H
R

55


Ph
7] 55
N

R


Ph

uH- 7 base
N

R

57


R
I
Ph N
KMe
C(Ph)N-Me
R

59


R = t-Bu, Me


ylide (56), would produce aziridine 57, in a manner which

is exactly analogous to the reaction of the N-tert-butyl


Ph
HCH2

R

56








ketiminium salt videe supra). Although the abstraction

of a proton on an aziridine ring is known to be a difficult

process,26 it is conceivable that deprotonation of 57 would

produce an aziridinyl anion, which could condense with

another molecule of the aldiminium salt. The product would

be the observed aminomethylaziridine, 58. Proton transfer

(presumably stepwise) would afford the diaminostilbene, 59.

To test Mechanism A for the case R=t-Bu, the known16

aziridine 39 was treated with the silylamide base in benzene.

As depicted in Scheme VIII, addition of deuterium oxide

after one hour failed to produce the deuterium-exchanged

product 60 (as evidenced by nmr spectroscopy). Similarly,


Scheme VIII

Ph


Ph N D
D20 I
NaN(SiMe3)2 t-Bu
N benzene 60
t-Bu r.t., N2

39 14a
50 + 52 (+39)



inclusion of 39 in the reaction mixture of the aldiminium

salt 14a, base, and benzene, afforded only the "normal"

reaction products. Aziridine 39 was recovered intact.

Finally, it was shown that the major isomer of the amino-

methylaziridine 50 could be recovered unchanged, after









Scheme IX

MECHANISM B


Ph H Ph
SCH, bse J*/,CH
K. OH2 -yse +H2
H H N
R R
55 56


R
Ph I
H N Me
Ph -N CH
H
R


base


Ph
+ N-CHI- 55
SH -N
I
R
61


path
2
59 -
- base


11
2 R
PH-N e path
H N Me
~CH2-H base
Ph I

R
63


R = t-Bu, Me


58








stirring it with the base in benzene at room temperature.

In particular, there was no evidence for the conversion

of major-50 to 52, the last step in the proposed Mechanism

A.

According to the second mechanism, outlined in Scheme

IX, the resonance-stabilized azomethine ylide 56 would be

generated, as per Mechanism A. However, since it is not

unreasonable to expect that the carbon terminus of the

ylide bearing the phenyl group should have the greatest

anionic character, it is conceivable that reaction of the

ylide (as 61) with 55 would produce intermediate 62. De-

protonation of 62, or initial tautomerization followed by

deprotonation via paths 1 and 2, would afford the observed

products. A somewhat disturbing aspect of Mechanism B is

the unlikelihood that the initial intermediate would react

exclusively in the canonical form 61. Indeed, steric factors

favor form 56, with its less-hindered reactive terminus, and

it is well known that steric effects can overwhelm electronic


t-Bu
t- t-Bu
Ph |
H N Ph N
Me NMe

H Ph CHN-t-Bu
H N
I u CH2Ph
t-Bu


64 65





35
2i,5b
preferences for regioisomeric transition states.2
However, resonances which could be attributed to 64 and
65, derived from the condensation of 56 with salt 12a
(assuming Mechanism B), were not detected in the nmr
spectrum of the crude product mixture. In addition, it
is difficult to explain the failure of 12a to cyclize to
aziridine 39 after deprotonation, if this second mechanism
were operating.
Mechanism C, then, postulates initial abstraction of
the vinylic proton of 55 to afford the azavinylic anion
66, as indicated in Scheme X. There are many reports in


Scheme X

MECHANISM C

SR
Ph Ph Ph
Si. Me base Me 55 N Me

I Ph
R R I
R
55 66 63


R=t-Bu
R = t-Bu, Me R=-B
-L base
Ph

H 58 +59
I
t-Bu

39








the literature which attest to the acidity of protons in
27
related environments. Nucleophilic attack by 66 on

the iminium salt would produce intermediate 63, which is

common to the preceding mechanism. As it was demonstrated,

63 can react to produce the observed products 58 and 59.

Mechanism C offers an attractive explanation for the obser-

vation that aziridine 39 is not a product of the reaction

of 12a with the base: as shown in Scheme X, 39 can not be

formed directly from intermediate 66 (R=t-Bu). Furthermore,

this last mechanism avoids the regioselectivity problem

associated with Mechanism B.

In both Mechanisms B and C, the common intermediate 63

can serve to account for the different product distributions

obtained by deprotonation of the tert-butyl- versus the

dimethyl-aldiminium salt. The methine proton of 63 is

effectively acidic only when its bond to carbon lies in a

plane which is orthogonal to the general plane of the iminium

moiety (geometry 67). Since bulky R groups on both nitrogen

atoms are likely to discourage such a geometry, due to steric

interactions, reaction via path 1 (Scheme IX) should be more

predominant for the case R=t-Bu than for the case of the less-

hindered dimethyl intermediate (R=Me), which should more

easily accommodate geometry 67 (and, hence, experience more

favorable competition by path 2). The result would be a

higher ratio of 58 to 59 for R=t-Bu than for R=Me, as ob-

served. Note, too, that the disposition of the amine and

phenyl substituents on the chiral carbon atom of 63 determines



































whether the E- or the Z-diaminostilbene is produced: 67

has been drawn such that the former would result. From

steric considerations, this disposition is less critical

for R=Me than for R=t-Bu, since the latter intermediate

must orient itself to minimize nonbonded interactions

between tert-butyl groups. Thus, one would predict that

14b should produce a more equal distribution of E- and Z-

isomers than would 14a. This last prediction was confirmed

by experiment, too, as was described earlier.

The problem of differentiating experimentally between

Mechanisms B and C is a difficult one. It is complicated

by the potential interconversion of the initial inter-

mediates in the two mechanisms (equation 14). As a result,

success in demonstrating the intermediacy of either of








Ph

+1 +CH2 ..
H N
I


Ph

S+ /Me
- NN

R


these species could not be construed as firm evidence for
either of the two mechanisms. However, a novel experiment
which might lend support to one or the other of the mecha-
nistic possibilities is proposed in Scheme XI. Consider

Scheme XI


MECHANISM
C
base


Ph
+- + Me
r-31"'


Ph

IN Me

cc


I
base 'MECHANISM
B


Ph
HNCKH2

E


PhCH=NCH2CH2CH=CMe2

_Pr" 72


- r


~E---- ,


Ph

H CH


73


Norbornene was found to be ineffective as a trapping
agent for any of the intermediates derived from salt 14a.


H Ph


S------ N7CH2

74








the deprotonation of the dimethylallyl salt 68, a reason-

able steric and electronic approximation of the tert-

butyl aldiminium salt. If Mechanism B were operating,

abstraction of an N-methyl proton from 68 would provide

intermediate 71. A thermally allowed [2,3] anionic

sigmatropic rearrangement of either 71 or its resonance

contributor, 73, would afford products 72 and 74, respec-

tively. There is ample literature precedent for similar

rearrangements.28 Alternatively, the operation of Mechanism

C would be suggested by the production of ketimine 70, the

result of another rearrangement of the azavinylic anion 69.

The starting material, compound 68, should be made avail-

able by methylating the imine derived from benzaldehyde and

the appropriate allylamine.29

The origin of the asymmetric bias that produced the

two diastereoisomers of aminomethylaziridine 50 is open to

speculation, because the energy difference between two

diastereomeric transition states is usually very small.

One argument for the supposed predominance of isomer 50a

is outlined in Scheme XII. Assume that Mechanism C is

operating. Attack by the azavinylic anion on the si-face

of the iminium salt, for example, would afford inter-

mediate 75, having the rectus configuration. Deprotonation




For example, on the order of 0.1-5 kcal/mol for
cycloaddition reactions; see reference 5b.
**
Although attack on the re-face is equally probable,
the eventual aminomethylaziridine is simply the enantiomer
of 50a.







of 75 would produce azomethine ylide 76, which has been
drawn in a probable conformation.2i Although there are


Scheme XII


Me
Ph I
\t-Bu


t-Bu+O C oH
Me~Uj Ph


Me
Ph I
Me \t-Bu
Mejl-Ph
I HtB
t-Bu


base


t-Bu


/ NN
Me
Ph t-Bu


76 500




two topologically distinct conrotatory modes of ring
closure available to all electrocyclic transition states,30
it is known that steric factors ("secondary orbital inter-
actions") play a large part in determining the preferred
mode. It is suggested that the conrotatory mode shown
for 76 would predominate, to circumvent the steric









interaction of the dipolar tert-butyl substituent with

the phenyl group on the aminomethyl side chain. The

relative configuration of the product, 50a, would be

the same as that assigned to the major diastereoisomer

from nmr spectral considerations videe supra). The

opposite mode of conrotatory ring closure would provide

the supposed minor isomer of 50.

The pyrolyses of both diastereoisomers of 50 to

produce the same diaminostilbene (52) is, at least

formally, the result of thermally allowed conrotatory

ring openings to form the respective enantiomeric ylides

77a and 77b, followed by [1,4] anionic shifts of the

methine protons, as shown in Scheme XIII. Chapman and

Eian have published a similar example of the latter

process. The intermediacy of azomethine ylides 77a and

77b is supported by the experimental observation that

pyrolysis of major-50 also produces some minor-50, and

vice versa. Since the thermolytic ring openings of aziri-

dines are generally reversible processes (equation 1), it

is certainly possible that one isomer of 50 could epimerize

partly to the other via an ylide intermediate.








*
More accurately, configuration 50a is converted to
the enantiomer of configuration 50b (but still the minor
isomer).









Scheme XIII


MAJOR ISOMER
50a


MINOR ISOMER
50b


A


A


Ph
.-N(Me)t-Bu


t-Bu--
I


[o-2s + r2 s+ w2s]

77a






Ph
-N(Me)_t-Bu

-u"M Ph
t-Bu Me

[o-2s + 7r4s]


77b














CHAPTER II

APPROACHES TO THE SYNTHESIS OF THE 2-AZIRINE SYSTEM



Introduction

Synthetic and theoretical chemists have long been

fascinated by the 2-azirine system, 78. Despite claims

for the intermediacy of 78 in mass spectral fragmentations32

and chemical reactions,33 and despite several spurious

reports of the isolation of derivatives of 78,34 the

synthesis of an authentic 2-azirine has not been achieved.






N
N


78 79


The failure to prepare a stable 2-azirine can not be

attributed to inordinate strain within the molecule, since

the isomeric 1-azirines (79) are well-known compounds.35

Therefore, it seems likely that the alleged instability of

78 can be attributed to an unfavorable electronic situation.

Indeed, theoretical interest in 2-azirines derives from the

theory that they are potentially 4i-electron anti-Huckel








systems,36 isoelectronic with the cyclopropenyl anion,36a

which should be destabilized by cyclic conjugation. Simple

Hiickel molecular orbital calculations predict a destabili-

zation energy of 0.308 for the parent 2-azirine, relative

to its open-chain analog, enamine.37

In principle, there are two major geometries that the

2-azirine system can adopt. In one geometry, 80, the non-

bonded electrons on the nitrogen atom occupy the unhybridized

2pz orbital, resulting in a conformation in which the

nitrogen substituent is coplanar with the three-membered

ring. Alternatively, the predicted unfavorable electronic











80 81


situation in 80 can be alleviated to some extent if the

nitrogen atom assumes sp3-hybridization, thereby minimizing

interaction of the nonbonded electrons with the carbon-

carbon i-system. This results in the nonplanar (and non-

aromatic) conformation, 81. In addition to electronic

considerations, the strained three-membered ring should

more easily accommodate the E 3-hybridized nitrogen atom

of 81, with its smaller endocyclic valence angle. Recent

calculations by Clark38 predict that the nitrogen substituent








should deviate from the plane of the 2-azirine ring by

68*, and that the barrier to nitrogen inversion should

be 35.14 kcal/mol. This sizable barrier ostensibly

reflects the instability of the planar transition state

for inversion, geometry 80. Clark's calculations have

been substantiated recently by those of Dewar and Ramsden.39

The synthesis of the 2-azirine system has been

attempted from two directions: (1) direct synthesis of

the three-membered ring, and (2) modification of an intact

three-membered ring. With regard to the first strategy,

the most common approach has been via the addition of

nitrenes to acetylenes. A relatively "early" (1963)

application40 of this approach involved the attempted

matrix isolation of 82 by the addition of singlet nitrene



argon H H
matrix
:NH + HC=CH -----/ N (15)
40K
H

82


to acetylene, as shown in equation 15. The only product

which was detected, however, was ketenimine (H2C=C=NH).

The intermediacy of a 2-azirine was first claimed by Rees

and his colleagues, based on the nitrene approach.33a,d

Other attempts41 to add nitrenes to acetylenes have

failed to produce evidence for the existence of 78.







33b,c,e
More recent work from Rees' group, outlined
in Scheme XIV, has provided the most convincing evidence
for the intermediacy of the 2-azirine system to date. It
was found that the same products and product ratios were



Scheme XIV


Me
Me N/
Ph
R
83


Ph
N
Me
R
84


/
Me
R N Ph

N


Me

N

R


85



Ph

R
N


R= 2-phthalimido








obtained by vapor-phase flash photolysis of the isomeric

triazoles 83 and 84. Since it was demonstrated that

there was no interconversion between the two starting

materials, or between the products 86 and 87, a common

intermediate was indicated. The authors assigned to this

intermediate, structure 85. Related work on the triazole

system by Burgess et al.42 failed to produce evidence for

a 2-azirine intermediate.


Scheme XV


H




R

88

41




It




+ N
I Y
R

91


bose
-HX







N
I

R

90


base I
-HY


X = good nucleophile
Y = poor nucleophile


RX
r------*



I

H


N


89



I RY







Synthetic approaches to the 2-azirine system that are

based on modifying an existing three-membered ring are
shown in Scheme XV. The strategy of using substituted

aziridines (88) as potential 2-azirine precursors has been
43
tried, for example, by Deyrup and Greenwald.43 As out-
lined in Scheme XVI, treatment of 92 with potassium tert-

4butoxide afforded hydrocinnamanilide (94) as the major


Scheme XVI



Me H
S 0-u H2C Ph Ph
CI Ph K O--Bu 7 "..
N -HCI N Y
I P -r

Ph Ph N-Ph

92




Me Ph 0

N NPhN ph

Ph H

93 94


reaction product, the apparent result of a heteromethylene-

cyclopropane rearrangement. The authors found no evidence

for compound 93. Similar approaches involving monochloro-
aziridines37 and aziridine esters44 have also been
aziridines and aziridine esters have also been







unsuccessful in preparing the 2-azirine system, as has
45
the sequence indicated in equation 16.45 As a final
example, Rubottom et al.46 have recently reported the


H

0 \ t I) PhMgBr
\ t-Bu |u
N 2)NH4CI

Ad
Ad


Ph H


HO '/"t-Bu
N -
Ad
Ad


Ph t-Bu


N
I
Ad


Ad = 1-adamantyl


H CI

NoH
Ar N CI HMPA
or
DME
Ph


CI
Ar -l AgC04 Ar CI


N -78 N
Na I I
Ph Ph


synthesis of a stable aziridinyl C-anion (95), which,

instead of being converted to 96, produced a "living

polymer"(!) upon treatment with silver perchlorate.

With the added purpose of better defining the scope

of the iminium salt deprotonations described in Chapter I,








it was proposed that potential 2-azirine precursors

of type 88 might be accessible via the deprotonation

of those iminium salts (97) which were substituted with

good leaving groups (X), as shown in Scheme XVII. Based


Scheme XVII


Me Y ,I M
X N X ------- x N
I I
R Y R

97


H


x
R


rH


I

R


base
-HY


-------------31


-HX
-- -----


N

R


on the successful alkylations described in the preceding

chapter, two likely candidates for 97 were compounds 98

and 99. The former compound, in addition, offered the

possibility of producing an aziridine intermediate which

was sufficiently stable to the reaction conditions to











Ph Ph

+ k
EtO N(Me)Ph Ci 'N(Me)Ph


OS02CF3 OSO2F



98 99



enable its isolation. The isolation of 2-alkoxyaziridines

under strongly basic conditions has been reported, for
47
example, by Sato.4

A second approach to the synthesis of 2-azirines from

intact three-membered rings involves the isomerization of

1-azirines (89, Scheme XV). In most of the reported

cases, the 1-azirines were used as precursors to aziridines

of type 88. It is not unlikely that the failure of this

approach has been due, at least in part, to the relatively

high nucleophilicities of the potential leaving groups

attached to 88. Accordingly, the cyclic iminium salts 91

(in which Y is a very poor nucleophile) were envisioned

as suitable precursors to 90. The other synthetic approach

to the 2-azirine system which will be described in this

chapter, then, will involve the attempted generation and

deprotonation of alkylated 1-azirines.

Although 1-azirines have been protonated,48 attempts








to alkylate them have generally met with failure (owing

to the low nucleophilicity of the 1-azirine nitrogen

atom3537). For example, compounds 100b and 100d were

found to be unreactive toward methyl iodine and benzyl

chloride in refluxing acetone.37 It was hoped, however,



R
Ph a, R=H

SP b, R Ph
N
c, R = C02Et


00 d, R =Me




that the very potent alkylating agent, methyl triflate

(acting as RY in Scheme XV), would ensure alkylation of

the 1-azirines. The three compounds that were used to

test this approach were the known azirines 100a, b, and

c. These particular ones were chosen largely on the

basis of their synthetic accessibility and relative

thermal stability.



The Aziridine Approach

Results

The required a-alkoxyiminium salt 98 was prepared in

91% yield by the 0-alkylation of N-methylbenzanilide

(101) with ethyl triflate, as shown in Scheme XVIII. The

product is a white solid which can be recrystallized from









Scheme XVIII




HN(Me)Ph CFgSO20Et
PhCOCI H------ PhCON(Me)Ph CF3S
10% NaOH r.t., N2
101




Ph Ph


Eto + EtO IN

Ph Me

OS02CF3 OS02CF3


98a 98b



absolute ethanol. Its NMR SPECTRUM 20 clearly indicates

the presence of the two configurational isomers, 98a and

98b.

Synthesis of a model a-chloroiminium salt was

attempted first by treating amide 101 with thionyl chloride,

as shown in equation 18. The major reaction product, how-

ever, was the imidoyl chloride 103, formally the result of
49
a von Braun degradation49 of the desired iminium salt 102.

It was subsequently found that 103 could be alkylated in

moderate (46%) yield with methyl fluorosulfonate, as shown










Ph


CI NPh


103


102


in Scheme XIX. Data taken from NMR SPECTRUM 21 of the

product suggest a single isomer, presumably structure

99.


Scheme XIX



PhNH2 SOCI2
PhCOCI -h2 PhCONHPh ----
10% NaOH


Ph

C I- NPh


FSO2OMe
r.t., N2


Ph
+ -Me
I -
Ph OS02F


103


Results of the deprotonation experiments were dis-
appointing. Treatment of the a-ethoxyiminium salt 98
with potassium tert-butoxide in ether at -78" afforded


10 SOC2
I0 1 -- -








only ethyl benzoate, N-methyl aniline, and N-methylbenz-

anilide (101) in a molar ratio of 1:1:0.8 (equation 19).

The reaction of 98 with sodium bis(trimethylsilyl)amide

in benzene at 0 produced a mixture in which nothing

could be identified.


Ph
,* KO-t-Bu
EtO'N(Me)Ph ethe PhCO2Et + HN(Me)Ph + 101
ether

OS02CF3 -78, N2
98 (19)
98


Similarly, treatment of salt 99 with NaN(SiMe3)2 in

benzene produced a dark oil, whose nmr spectrum indicated

a complex mixture. Repeated attempts to separate com-

ponents of the mixture by column chromatography were un-

successful.

Discussion

In view of the paucity of information about the

products that were formed in these deprotonation reactions,

one can not rigorously justify the apparent failure of this

approach. It can not even be assumed, for example, that

deprotonation took place at all! Indeed, although one

would expect the inductive effect (104) of the hetero-

substituent of compound 97 to enhance the acidity of the

N-methyl protons, the resonance contribution (105) should

render these protons less acidic, in addition to making

the a-carbon atom more electrophilic. At least in the case









Ph
1 Me


Ph


Ph

P ,Me
x IP
Ph


104


Ph
N "NMe
+ I
Ph


105


of the reaction between the a-ethoxyiminium salt 98 and
potassium tert-butoxide, it is possible to explain the
results obtained by postulating first nucleophilic attack
by the base, followed by collapse of the resulting ketal



Scheme XX


Ph
L + t-BuO-
Et N(Me)Ph -- -
EtO


path

Me
Ph
N Ph
N ph
0

I01


Me
Ph N
N Ph
EtO

0"' H
Me Me

106


path 2


PhC02Et + HN(Me)Ph








106 to produce the observed products, as shown in Scheme

XX. Of course, one can not exclude the possibility that

these products resulted, at least in part, from simple

hydrolysis by traces of moisture in the reaction mixture.

Also, there is some precedent for the Chapman rearrange-

ment of compounds such as 98 to afford amides corresponding

to 101.51

The unpromising results of this aziridine approach

to the synthesis of the 2-azirine system prompted the

investigation of the second approach, which was outlined

above.



The 1-Azirine Approach

Results

Two of the 1-azirines used in this study, compounds
52a 52b
100a and 100b, were prepared according to published

procedures52 by pyrolysis of the corresponding vinyl azides

(107), as shown in Scheme XXI. The 3-carbethoxy derivative

100c was prepared by the thermal rearrangement of isoxazole

108, according to the procedure of Nishiwaki.53

All alkylations were performed in a nitrogen-purged

drybox. The addition of two drops of methyl triflate to




There is ample published precedent for the formation
of intermediates of type 106 from a-chloroiminium salts
(e.g., see reference 50); also, recall the major product
(48) of the reaction of aldiminium salt 14a with potassium
tert-butoxide (Scheme V, p 23).










Scheme XXI


NaN3
DMSO


I H

S N.Ph
R N3


N'No OEt


Br

SPh
Br


R

2000 H Ph
N


108


100o, R =H
b, R = Ph
c, R = COEt


neat 2-phenyl-l-azirine (100a) resulted in an immediate

explosion! The reaction mixture smoked and blackened

before collapsing to an intractable tar. Less stringent

conditions were tried: a 0.5 M solution of 100a in carbon

tetrachloride was frozen at -780, and an equimolar

solution of methyl triflate in dichloromethane (a liquid


Br
Ph

N3

NaOH DMSO


R Ph
KO-t-Bu
-HI
H N3

107, R = H, Ph


A -N2


R =H Br2


H Ph


R H

R= H, Ph


R = Ph
"IN3"


Ph
/hI) POCI3
N,0 0 2) NaOEt








at -78*) was layered onto the first solution. Upon

thawing and mixing, however, the system darkened. It

gradually deposited a black oil, which was not investi-

gated further.

The two-phase technique was next tried with 2,3-

diphenyl-l-azirine, compound 100b. Initially, the frozen

solution of 100b in carbon tetrachloride showed no visible

evidence of reacting with the methyl triflate solution at

low temperature. It was only after allowing the mixture

to warm to ambient temperature, and stirring for several

hours, that bright yellow crystals precipitated from the

solution. Elemental and spectral characterization of the

isolated solid suggested structure 109 in Scheme XXII (two

crops afforded 46% of the theoretical yield). For example,

NMR SPECTRUM 22 of the product showed a deshielded, three-

proton singlet at 63.31, and a one-proton singlet at 66.34.

These were assigned to the methyl and vinyl protons of 109,
*
respectively. As shown in Scheme XXII, this structural

assignment was substantiated by treating compound 109 with

dilute, aqueous sodium hydroxide. The free base (110, NMR

SPECTRUM 23) was produced in quantitative yield. Reproto-

nation of 110 with trifluoromethanesulfonic acid returned

compound 109. In addition, 109 was converted to the alkyl-

ated pyrazine 111 (NMR SPECTRUM 24) by refluxing it with




Cf. the following data on the corresponding protons
of the free base, 110 videe infra): 62.98 (singlet, 3H,
CH3) and 5.78 (singlet, 1H, vinyl).









Scheme XXII


Ph
^HPh

N

IOOb

CCl4-CH2Cl2
CF3SO2OMe -
-780,N2

Ph Ph H


H N M e
Ph Ph -
OS02CF3
5% 109
CFaSOgO0H
NaOH

HO* IEtOH


Ph Ph Ph N Ph
N NMe Ph Ph CFSOOMe N Ph
"| |P+Ph N Ph
Ph Ph Me -OSOCFa

110 112


dilute, aqueous hydrochloric acid in ethanol. Product 111,
in turn, was found to be identical (by nmr spectral com-
parison and mixture melting point determination) to that
obtained by the alkylation of an authentic sample of tetra-
phenylpyrazine (112)54 with methyl triflate.
phenylpyrazine (112) with methyl triflate.









The alkylation of azirine 100b was repeated in a

sealed nmr sample tube, using a CCl4-SO2 solvent system.

Periodic nmr spectral assay of the homogeneous system

after it had warmed to room temperature (defined as

time t ) revealed that most of the 1-azirine was consumed

within one hour after t_. The diazatriene 109 was formed
-o'
between 2 and 3.5 hours after t It began to decompose

24 hours later, however, to what was apparently the

alkylated pyrazine, 111.

The 3-carbethoxy azirine 100c was also subjected to

the two-phase alkylation conditions. Spectroscopic assay

of the reaction mixture one day after the addition of the

methyl triflate indicated that little reaction had taken

place during this period. The azirine was totally consumed

within one week, however, but the decomposition products

were not identified.

Discussion

The formation of 109 from 100b can be explained by

several related mechanisms, one of which is suggested in

Scheme XXIII. Alkylation of the 1-azirine would produce

the cyclic iminium salt 114. In preference to deproto-

nation, thereby generating the 2-azirine 115, intermediate

114 could open to form the more stable aza-allylic cation

(113). There are several literature precedents for the




The behavior of two additional, unidentified res-
onances is described in Chapter III, p 121.








cleavage of aziridinyl cations such as 114.26

Alkylation of 113 by a molecule of the intact azirine

would afford 116 which, by another ring opening and

tautomerization, would produce the observed product,

109. Formation of the pyrazinium salt 111 from 109

probably takes place via intermediate 117, followed by

spontaneous air oxidation, as shown in equation 20.




S Ph


109 H 1N H 10) 111 (20)
Ph I
Me OS02CF3


117


Although azirine 100c was chosen for study partly

with the expectation that its ester substituent would

discourage formation of the cation corresponding to 113,

there is no evidence that this effect was responsible for

the sluggish reaction of 100c with methyl triflate.

Rather, it is likely that the electron-withdrawing effect

of the ester group deactivated the azirine nitrogen atom

to alkylation. Nishiwaki et al. have made similar ob-
.53b
servations.















CHAPTER III

EXPERIMENTAL



Melting points were determined with a Thomas-Hoover

Unimelt capillary melting point apparatus and are un-

corrected. All temperatures are given in C. Infrared

spectra were recorded with a Perkin-Elmer Model 137

spectrometer. Nuclear magnetic resonance (nmr) spectra

were recorded on a 60 MHz Varian Associates A-60A high-

resolution spectrometer at a sweep width of 500 Hz.

Chemical shifts (6) are reported in parts per million

downfield from internal tetramethylsilane standard. Low-

resolution mass spectra were measured on either an Hitachi

Perkin-Elmer RMU-6E spectrometer or an AEI-MS-30 double-

beam instrument. Microanalyses were performed by Atlantic

Microlab, Inc., Atlanta, Georgia.

Thin-layer chromatography (tlc) was accomplished with

Eastman Silica Gel Chromagram Paper with fluorescent indi-

cator. Results were visualized by exposure to ultraviolet

light and iodine vapor. Solvent evaporations were performed

with a Buchler rotary evaporator equipped with a water

aspirator. Except as noted, the syntheses, isolations and

reactions of moisture-sensitive compounds were effected in

a Labconco (Kansas City, Missouri) fiberglass drybox purged









with dry nitrogen and equipped with an aspirator for

suction filtration. All glassware used in the drybox

was dried in an oven (ca. 100) for at least eight

hours.

All reagents were used as purchased and were Reagent

Grade, unless otherwise indicated. Anhydrous solvents

were generally prepared by drying over Linde molecular

sieves, size 3A or 4A.


General Procedure for the Preparation of the Ketimines

(9). The ketimines (9) were prepared by slight modifica-

tion of the method of Moretti and Torre.0 A three-necked

2000-ml round-bottomed flask was equipped with a 250-ml

pressure-equalized addition funnel, gas inlet, and reflux

condenser with a Drierite drying tube. The entire apparatus

was flamed with a Bunsen burner while being purged with dry

nitrogen. The flask was then cooled with an ice bath, and

a thermometer and magnetic stirrer were inserted. To the

flask was added a solution of benzophenone (Eastman, 18.22 g,

0.100 mol) and a tenfold excess of the appropriate amine

in dichloromethane (500 ml). Next, a solution of titanium

(IV) chloride (Ventron, 12.4 g, 7.2 ml, 0.065 mol) in di-

chloromethane (200 ml) was added dropwise over a period of

ca. 60 minutes, while maintaining the temperature below 5.

The mixture was stirred at room temperature for 3-6 days,

while monitoring the progress of the reaction by infrared
CCI -1
spectral assay (vC l4 ca. 1620 cm ) of aliquots. When
the reaction was complete, the mixture was filtered through
the reaction was complete, the mixture was filtered through









glass wool. The filtrate was washed with saturated sodium

chloride, treated with anhydrous magnesium sulfate and

activated charcoal, and concentrated in vacuo to afford

the crude ketimine (9). If necessary, the products were

purified by distillation or recrystallization.


N-(Benzhydrylidene)tert-butylamine (9a). N-(Benzhydrylidene)-

tert-butylamine (9a)10 was prepared according to the general

procedure from tert-butylamine (MC/B Manufacturing Chemists,

69.6 g, 100 ml, 0.95 mol). The mixture was stirred for six

days. Work-up afforded the crude 9a (22.0 g, 93%): mp 33.5-

35.5" (lit.10 35-36); nmr (CC 4) 61.13 (singlet, 9H, tert-

butyl), 6.9-7.6 multiplee, 10H, aromatic).


N-(Benzhydrylidene)methylamine (9b). This compound was

prepared in the usual manner from methylamine hydrochloride

(MC/B, 67.5 g, 1.00 mol) and triethylamine (101 g, 139 ml,

1.00 mol). The mixture was worked-up after one week to

afford the crude product (18.7 g, 96%). Bulb-to-bulb

distillation (0.10 mm) with a rotary evaporator and a Bunsen

burner produced the pure N-(benzhydrylidene)methylamine

(9b,10 16.7 g, 85%) as a clear, colorless oil: nmr (CC14)

63.15 (singlet, 3H, CH3), 6.9-7.7 multiplee, 10H, aromatic).


N-(Benzhydrylidene)allylamine (9c). This compound was

synthesized from allylamine (Eastman, 57.1 g, 75 ml, 1.00

mol) according to the general procedure. Work-up after

stirring the mixture for 18 hours afforded the crude product

(20.5 g, 93%) as a viscous, orange oil. The material was









distilled (0.05 mm) with a rotary evaporator and Bunsen

burner to afford the pure N-(benzhydrylidene)allylamine

(9c)56 as a clear, pale yellow oil: nmr (CC14) 63.8-4.1

multiplee, 2H, allyl), 4.8-5.3 multiplee, 2H, =CH2),

5.7-6.3 multiplee, 1H, CH2=CH), 6.9-7.8 multiplee, 10H,

aromatic).


N-(Benzhydrylidene)benzhydrylamine (9d). The general

procedure for the preparation of the ketimines was

followed on a 0.050 mole scale, using dry benzene (instead

of dichloromethane) and benzhydrylamine (Aldrich, 96%,

91.6 g, 0.480 mol). The mixture was worked-up after three

days, and the excess amine was removed by washing a solution

of the crude product in ether (300 ml) with 2% aqueous

hydrochloric acid (2x200 ml). The resulting interfacial

solid was combined with the ethereal extract, and the

solvent was removed in vacuo. The dried, pure white prod-

uct (10.9 g, 63%) melted at 150.5-152* (lit.57 154) and

showed the following nmr spectrum (CDC13): 65.56 (singlet,

1H, benzhydryl), 6.9-7.9 multiplee, 20H, aromatic).


N-(Benzhydrylidene)aniline (9e). N-(Benzhydrylidene)aniline

(9e)5 was prepared from aniline (Mallinckrodt, 93.1 g, 91

ml, 1.00 mol) in the usual manner. The mixture was worked-

up after five days, and the crude product was recrystallized

from absolute ethanol to produce pure 9e (20.7 g, 81%): mp

112-113' (lit.58 117"); nmr (CCl4) 66.4-7.8 multiplee,

aromatic).









N-(Fluorenylidene)methylamine (18a). The general pro-

cedure for the preparation of the ketimines was modified

for the preparation of compound 18a. A solution of

methylamine hydrochloride (MC/B, 33.8 g, 0.500 mol) and

triethylamine (freshly distilled, 50.6 g, 70.0 ml, 0.500

mol) in dichloromethane (250 ml) was added to a solution

of fluoren-9-one (MC/B, 9.01 g, 0.050 mol) in dichloro-

methane (100 ml). After the addition of molecular sieves

(3A, ca. 5 g), the stirring mixture was cooled to 0-5,

and a solution of titanium (IV) chloride (6.2 g, 3.6 ml,

0.033 mol) in dichloromethane (100 ml) was added over a

period of 30 minutes. The usual work-up after five days

afforded crude N-(fluorenylidene)methylamine (18a, 8.87 g,

92%) as a clear, dark amber oil: nmr (CC14) 63.68 (singlet,

3H, CH3), 6.6-7.9 multiplee, 8H, aromatic).


N-(Fluorenylidene)tert-butylamine (18b). N-(Fluorenylidene)-

tert-butylamine (18b) was prepared as follows: a solution

of titanium (IV) chloride (6.2 g, 3.6 ml, 0.033 mol) in

dichloromethane (100 ml) was added over a period of 30

minutes to a stirring solution of fluoren-9-one (9.01 g,

0.050 mol), tert-butylamine (34.8 g, 50 ml, 0.48 mol), and

dichloromethane (350 ml), at 0-5. Conventional work-up

after two days afforded crude 18b (10.9 g, 92%) as a yellow

powder: mp 52-55"; nmr (CC14) 61.58 (singlet, 9H, tert-

butyl), 7.0-7.9 multiplee, 8H, aromatic).


General Procedure for the Preparation of the Ketiminium








Salts (12 and 13). A 500-ml round-bottomed flask was

equipped with a magnetic stirrer, placed in a drybox,

and charged with the appropriate ketimine (9, 0.05-0.08

mol) and dry solvent. The flask was immersed in a Dry Ice-

acetone bath and treated with approximately two equivalents

of the appropriate alkylating agent. The cold bath was

removed, and the system was stirred overnight at ambient

temperature. The ketiminium salts thus prepared were

collected by suction filtration in the drybox, washed with

ether, dried, and weighed.

In these and all succeeding alkylations, the methyl

fluorosulfonate (lla) was obtained from the Aldrich Chemical

Company, Inc. ("Magic Methyl," 97%); methyl triflate (lib)

was obtained from Willow Brook Laboratories, Inc. (Waukesha,

Wisconsin). Both materials were used without further puri-

fication.


N-(Benzhydrylidene)methyl-tert-butylaminium Fluorosulfonate

(12a). The general alkylation procedure was carried out

with a mixture of N-(benzhydrylidene)tert-butylamine (9a,

11.87 g, 50.0 mmol), methyl fluorosulfonate (lla, 10.6 g,

7.5 ml, 93 mmole), and anhydrous ether (75 ml). The crude

N-(benzhydrylidene)methyl-tert-butylaminium fluorosulfonate

(12a, 16.95 g, 97%) melted with decomposition at 125.

Three recrystallizations from absolute ethanol produced the

analytical sample of 12a: mp 128-128.5 dec; ir (Nujol)
-l
v1590, 1290, 1180, 1080 cm-1; NMR SPECTRUM 1 (SO2) 61.58

(singlet, 9H, tert-butyl), 3.78 (singlet, 3H, NCH3), 7.2-7.8








multiplee, 10H, aromatic); mass spectrum (15eV) m/e 41,

56 (base), 118, 194, 195; (70eV) m/e 77, 118 (base), 194,

195 (P+ 351 unobsd).

Anal. Calcd for C 8H22FNO S: C, 61.51; H, 6.31;

N, 3.99. Found: C, 61.40; H, 6.39; N, 4.02.


N-(Benzhydrylidene)methyl-tert-butylaminium Triflate (13a).

This compound was prepared by a modification of the general

alkylation procedure. Into a 25-ml round-bottomed flask

equipped with a magnetic stirrer was placed N-(benzhydryli-

dene)tert-butylamine (9a, 2.85 g, 12 mmol) and dry chloroform

(10 ml). The solution was stirred in an atmosphere of

nitrogen, cooled to 00, and treated with methyl triflate

(1.97 g, 2.00 ml, 12 mmol). The opaque mixture was stirred

at room temperature for 4.5 hours, and then concentrated in

vacuo. Trituration of the residue with anhydrous ether

produced a solid, which was collected by filtration, washed

with ether, and dried. The crude N-(benzhydrylidene)methyl-

tert-butylaminium triflate (13a) was isolated in quantitative

yield. It melted with decomposition at 113". Two recrys-

tallizations from ethanol-ether afforded the analytical

sample: mp 114-115.5" dec; nmr (DMSO-d6) 61.48 (singlet,

9H, tert-butyl), 3.68 (singlet, 3H, NCH3), 7.58 (ca. singlet,

ca. 10H, aromatic).

Anal. Calcd for C 9H22F3NO3S: C, 56.84; H, 5.52;

N, 3.49. Found: C, 56.75; H, 5.60; N, 3.48.


N-(Benzhydrylidene)dimethylaminium Fluorosulfonate (12b).








The general alkylation procedure was carried out with a

mixture of N-(benzhydrylidene)methylamine (9b, 15.6 g,

80 mmol), methyl fluorosulfonate (1a, 17.0 g, 12.0 ml,

150 mmol), and ether (200 ml). Additional ether (150 ml)

was added after the mixture had warmed to ambient tempera-

ture, to facilitate stirring. The usual work-up afforded

N-(benzhydrylidene)dimethylaminium fluorosulfonate (12b,

24.6 g, 100%) as a white powder, which melted at 131-142.

NMR SPECTRUM 2 (SO2) showed 63.86 (singlet, 6H, CH3), 7.6-

7.9 multiplee, 10H, aromatic).


N-(Benzhydrylidene)methylallylaminium Fluorosulfonate

(12c). Crude N-(benzhydrylidene)methylallylaminium fluoro-

sulfonate (12c, 16.47 g, 98%) was prepared from N-(benz-

hydrylidene)allylamine (9c, 11.07 g, 50.0 mmol), methyl

fluorosulfonate (lla, 10.6 g, 7.5 ml, 93 mmol), and ether

(100 ml), according to the general alkylation procedure.

Salt 12c melted at 83.5-91" and showed NMR SPECTRUM 3

(SO2): 63.80 (singlet, 3H, CH3), 4.71 (broad doublet,
J=ca. 5.8 Hz, 2H, allyl), 5.4-6.5 multiplee, 3H, vinyl),

7.4-7.7 multiplee, 10H, aromatic).


N-(Benzhydrylidene)methylbenzhydrylaminium Fluorosulfonate

(12d). The general alkylation procedure was modified for

the preparation of salt 12d. Into an oven-dried 50-ml

round-bottomed flask was placed N-(benzhydrylidene)benzhy-

drylamine (9d, 5.21 g, 15 mmol) and dry chloroform (35 ml).

The solution was cooled with an ice bath, purged with dry








nitrogen, and stirred magnetically. The ice bath was re-

moved after the rapid addition of methyl fluorosulfonate

(lla, 4.95 g, 3.5 ml, 44 mmol),-and the colorless solution

was stirred at room temperature for one hour. The chloro-

form and excess alkylating agent were removed in vacuo to

afford a viscous, pale yellow oil (9.83 g). Part of the

oil crystallized upon trituration with ethanol and ether at

-78*. The solid was collected by filtration and washed with

ether. The crude N-(benzhydrylidene)methylbenzhydrylaminium

fluorosulfonate (12d, 4.71 g, 68%) melted over a broad range

(ca. 109-140*). Three recrystallizations from ethanol-

ether produced 12d as a white powder, which melted at (162)

173-193' and showed NMR SPECTRUM 4 (DMSO-d ): 63.59 (singlet,

3H, CH3), 6.87 (singlet, 1H, benzhydryl), 7.2-7.8 multiplee,

ca. 20H, aromatic).


N-(Benzhydrylidene)methylanilinium Fluorosulfonate (12e).

The general alkylation procedure was applied to the synthesis

of salt 12e, starting with N-(benzhydrylidene)aniline (9e,

12.87 g, 50.0 mmol), methyl fluorosulfonate (lla, 10.6 g,

7.5 ml, 93 mmol), and ether (125 ml). Ketimine 9e was found

to be relatively insoluble in ether at -780, but the alkyl-

ation proceeded in the usual fashion. The crude N-(benz-

hydrylidene)methylanilinium fluorosulfonate (12e, 17.79 g,

96%) was obtained as a pale yellow powder: mp 215.5-220;

NMR SPECTRUM 5 (SO2) 64.22 (singlet, 3H, CH 3), 7.33 (ca.

singlet, 5H, aromatic), 7.51 (ca. singlet, 5H, aromatic),

7.73 (singlet, 5H, aromatic).









N-(Fluorenylidene)dimethylaminium Fluorosulfonate (19a).

The general alkylation procedure was followed on a smaller

scale for the synthesis of salt 19a. Addition of the

methyl fluorosulfonate (lla, 2.12 g, 1.5 ml, 19 mmol) to

the solution of N-(fluorenylidene)methylamine (18a, 1.93 g,

10 mmol) in dry chloroform (15 ml) produced an immediate,

voluminous, orange precipitate. Magnetic stirring was

facilitated by the addition of anhydrous ether (25 ml).

The mixture was stirred for 30 minutes, and the crude N-

(fluorenylidene)dimethylaminium fluorosulfonate (19a) was

collected by filtration, washed with ether, and pulverized

with a morter and pestle. The resulting pale orange powder

(2.83 g, 92%) melted at 220-233 dec. Compound 19a was

found to be insoluble in acetone (cf. salts 12 and 13).

Its nmr spectrum (SO2) showed 64.17 (singlet, ca. 6H,

CH3), 7.2-8.0 multiplee, ca. 8H, aromatic).


Pyrolysis of N-(Benzhydrylidene)methyl-tert-butylaminium

Triflate (13a). N-(Benzhydrylidene)methyliminium Triflate

(17). N-(Benzhydrylidene)methyl-tert-butylaminium triflate

(13a, 2.01 g, 5.0 mmol) was placed in a 2x20-cm Pyrex

pyrolysis tube equipped for quantitating gas evolution.

The tube was evacuated, filled with dry nitrogen, and

heated with an oil bath at about 130, until the volume of

collected gas (98 ml, ca. 90% of the theoretical amount of

isobutene) remained constant. Upon cooling, the melt

solidified. The pyrolysis tube was cracked open and the

crude N-(benzhydrylidene)methyliminium triflate (17) was








recovered in quantitative yield: mp 108-110; nmr (DMSO-

d6) 63.47 (singlet, ca. 3H, CH ), 7.70 (ca. singlet, ca.

10H, aromatic).


Attempted Alkylation of N-(Fluorenylidene)tert-butylamine

(18b) with Methyl Fluorosulfonate (lla). N-(Fluorenylidene)-

tert-butyliminium Fluorosulfonate (19b). Into an oven-dried

100-ml round-bottomed flask was placed N-(fluorenylidene)-

tert-butylamine (18b, 4.71 g, 0.020 mol) and dry chloroform

(30 ml). Methyl fluorosulfonate (lla, 4.24 g, 3.0 ml, 0.037

mol) was then added to the stirring solution at 0 in an

atmosphere of dry nitrogen. The dark mixture was allowed to

warm to room temperature, stirred for 15 minutes, and treated

with anhydrous ether (50 ml). The resulting dark red pre-

cipitate was collected by filtration. Two additional crops

were isolated from the refrigerated filtrates over a period

of three days. The total recovery of N-(fluorenylidene)-

tert-butyliminium fluorosulfonate (19b, 4.25 g) was 63%.

The third crop (1.34 g), for example, decomposed sharply

at 183* and showed the following nmr spectrum (SO2): 61.91

(singlet, 9H, tert-butyl), 7.2-8.2 multiplee, 8H, aromatic),

9.2-11.3 (broad singlet, ca. 1H, NH).


Attempted Alkylation of N-(Benzhydrylidene)tert-butylamine

(9a) with Ethyl Triflate. N-(Benzhydrylidene)tert-butylimin-

ium Triflate (20). A solution of N-(benzhydrylidene)tert

butylamine (9a, 4.75 g, 0.020 mol) in dry chloroform (20 ml)

was stirred magnetically in a 50-ml round-bottomed flask.









The system was purged with dry nitrogen and cooled with an

ice bath, after which ethyl triflate (Willow Brook Labora-

tories, Inc., 98%, 3.92 g, 0.022 mol) was added. The

resulting pale yellow solution was allowed to warm to

room temperature, and was stirred in an atmosphere of dry

nitrogen for 48 hours. The white precipitate that formed

during this time was collected by filtration, washed

with ether, and dried. N-(Benzhydrylidene)tert-butylimin-

ium triflate (20, 1.38 g, 18%) was found to melt with de-

composition at 1800. Two recrystallizations from absolute

ethanol afforded the analytical sample of 20 as fluffy,

white crystals: mp 178-179.5 dec; NMR SPECTRUM 6 (DMSO-d6)
-b6
61.40 (singlet, 9H, tert-butyl), 7.4-7.9 multiplee, 10H,

aromatic); mass spectrum (70eV) m/e 180, 222 (base), 237

(P+ 387 unobsd).

Anal. Calcd for C18H20F3N03S: C, 55.80; H, 5.20;

N, 3.62. Found: C, 55.70; H, 5.28; N, 3.58.


Pyrolysis of N-(Benzhydrylidene)tert-butyliminium Triflate

(20). N-(Benzhydrylidene)iminium Triflate (21). N-(Benz-

hydrylidene)tert-butyliminium triflate (20, 0.50 g, 1.3

mmol) was placed in an oven-dried 2xl5-cm Pyrex pyrolysis

tube equipped with a gas outlet which was connected to a

drying tube. The pyrolysis tube was immersed in an oil

bath to a depth of 4 centimeters. The system was heated

at 180-195, until gas evolution had ceased (about 15 min-

utes). Upon cooling, the clear, colorless melt solidified








as long white needles. The crude N-(benzhydrylidene)-

iminium triflate (21, 0.42 g, 98%) melted at 162-166*.

The analytical sample was obtained after two recrystal-

lizations from ethanol-ether: mp 167-169.5'; nmr (DMSO-d )

67.5-8.1 multiplee, ca. 10H, aromatic), 12.2 (broad

singlet, ca. 2H, NH2); mass spectrum (70eV) m/e 77, 105

(base), 182 (P+ 331 unobsd).

Anal. Calcd for C14HI2F3N03S: C, 50.75; H, 3.65; N,

4.23. Found: C, 50.50; H, 3.75; N, 4.15.


Treatment of N-(Benzhydrylidene)tert-butyliminium Triflate

(20) with Aqueous Base. N-(Benzhydrylidene)tert-butylamine

(9a). Into a 1.5xl5-cm test tube was placed N-(benzhydryl-

idene)tert-butyliminium triflate (20, 1.00'g, 2.58 mmol).

A solution of 10% aqueous sodium hydroxide (10 ml) was

added, and the resulting white gum was stirred magnetically

for five minutes. The mixture was extracted with dichloro-

methane, and the separated organic layer was washed with

water, dried with anhydrous magnesium sulfate, and concen-

trated in vacuo. The nmr spectrum of the residue (0.56 g)

was identical to that of authentic N-(benzhydrylidene)tert-

butylamine, 9a videe supra). The yield of the free base 9a

was 92%.


Treatment of N-(Benzhydrylidene)methyl-tert-butylaminium

Fluorosulfonate (12a) with n-Butyllithium (23). N-(Benz-

hydrylidene)methyl-tert-butylaminium fluorosulfonate (12a,

0.53 g, 1.5 mmol) was placed in a 25-mi round-bottomed








flask, in a drybox. To it was added with magnetic stirring

a solution of n-butyllithium (23) in hexane (MC/B, 15.1%,

1.00 ml, 1.7 mmol). An immediate, deep red color developed

(and persisted) during the addition of anhydrous ether

(10 ml). The mixture was stirred for one hour, removed

from the drybox, and filtered. The red filtrate turned

dark yellow upon exposure to the air. Evaporation of the

solvent in vacuo left a yellow oil (0.34 g) whose nmr

spectrum indicated a mixture which contained little, if any,

of the l-tert-butyl-2,2-diphenylaziridine (22, vide infra).


Treatment of 12a with 1,8-Bis(dimethylamino)naphthalene

(24). An oven-dried three-necked 25-ml round-bottomed

flask was fitted with a gas inlet, serum cap, drying tube,

and magnetic stirrer. To the flask was added N-(benzhydryl-

idene)methyl-tert-butylaminium fluorosulfonate (12a, 0.53 g,

1.5 mmol) and base 2420 (Aldrich, "Proton Sponge," 0.34 g,

1.6 mmol). The system was purged with dry nitrogen and

cooled to -78, and anhydrous ether (10 ml) was added via

the serum cap with stirring. The cold bath was removed

ten minutes after the addition, the serum cap was replaced

by a reflux condenser, and the off-white slurry was refluxed

overnight. The mixture was then filtered, and the ether-

insoluble material was found by nmr spectroscopy to be the

unreacted ketiminium salt, 12a (0.52 g, 98% recovered, mp

125-125.5 dec).








Treatment of 12a with Lithium 2,2,6,6-Tetramethylpiperidide

(25). A 50-ml round-bottomed flask was placed in a drybox

and charged with N-(benzhydrylidene)methyl-tert-butylamin-

ium fluorosulfonate (12a, 1.05 g, 3.00 mmol), 2,2,6,6-tetra-

methylpiperidine59 (0.44 g, 3.10 mmol), and anhydrous ether

(20 ml). A solution of 1.9 M n-butyllithium in hexane

(MC/B, 1.63 ml, 3.10 mmol) was then added with magnetic

stirring. The deep red mixture was stirred overnight,

during which time it changed to a light brown slurry. The

slurry was removed from the drybox and concentrated in

vacuo. Ether and water were added to the residue, and the

separated ethereal layer was washed with saturated sodium

chloride, dried with anhydrous magnesium sulfate, and evap-

orated to a viscous, amber oil (0.81 g). The nmr spectrum

of the oil indicated the presence of 2,2,6,6-tetramethyl-

piperidine [61.05 (singlet, CH3)] in addition to 1-tert-

butyl-2,2-diphenylaziridine (22) and N-(benzhydrylidene)-

tert-butylamine (9a). Estimation of the relative propor-

tions of the latter two compounds (ca. 0.7:1) was made by

comparison of the peak heights of their respective tert-

butyl resonances.


Treatment of 12a with Lithium 2,6-Di-tert-butylphenoxide

(26). A 25-ml round-bottomed flask equipped with a

magnetic stirrer was placed in a drybox, and into it was

placed a solution of 2,6-di-tert-butylphenol' (Aldrich,

min 99%, 0.41 g, 2.0 mmol) in anhydrous ether (10 ml).

To the stirring solution was added a solution of 1.9 M








n-butyllithium in hexane (1.00 ml, 1.9 mmol). The

resulting white slurry of lithium 2,6-di-tert-butyl-

phenoxide (26) was stirred at ambient temperature for

10 minutes; cooled with a Dry Ice-acetone bath, and

stirred for 15 minutes at -78'. N-(Benzhydrylidene)-

methyl-tert-butylaminium fluorosulfonate (12a, 0.56 g,

1.5 mmol) was then added rapidly. The mixture was

stirred at -78' for 15 minutes, and allowed to warm to

ambient temperature. After stirring for an additional

60 minutes, the insoluble material was collected by filtra-

tion, washed with ether, and found by nmr spectral analysis

to be the unreacted iminium salt 12a (0.40 g, ca. 70%

recovered, mp 118-118.5" dec). The combined filtrate and

washes were evaporated in vacuo to produce an oil (0.68 g),

which was shown by nmr spectroscopy to be a mixture of

which half (on a molar basis) was 2,6-di-tert-butylphenol

[61.40 (singlet, tert-butyl)]. The remainder of the

mixture was largely 22 and 9a in a ratio of 1.3:1.


Treatment of 12a with Sodium Dimsylate (27). A solution

of N-(benzhydrylidene)methyl-tert-butylaminium fluorosul-

fonate (12a, 5.27 g, 15.0 mmol) in dry dimethyl sulfoxide

(50 ml) was stirred in a 200-ml round-bottomed flask in a

drybox. A dispersion of sodium hydride in mineral oil

(Ventron, 57%, 0.85 g, 20 mmol) was then washed with ether,

and the washed sodium hydride was added as a.solution in

DMSO (50 ml) to the iminium salt solution. The tan mixture

was stirred at ambient temperature for four hours, during








which time it darkened appreciably. The system was re-

moved from the drybox, most of the solvent was removed

at reduced pressure, and the residue was treated with

ether. The ethereal solution was washed with water and

saturated sodium chloride, treated with activated char-

coal and anhydrous magnesium sulfate, and filtered through

Celite. Concentration of the filtrate in vacuo afforded

a yellow syrup (3.62 g). The syrup was triturated with

cold ether, and the resulting precipitate (0.31 g ) was

removed by filtration. The filtrate was evaporated in

vacuo to produce a clear, amber oil, whose nmr spectrum

indicated the presence of aziridine 22, imine 9a, and

benzophenone in the ratio of 1.8:1:0.2.


Treatment of 12a with Potassium tert-Butoxide (28) in

Hexamethylphosphoramide. A 25-ml round-bottomed flask

equipped with a magnetic stirrer, gas inlet, and drying

tube was placed in a drybox. The flask was charged with

N-(benzhydrylidene)methyl-tert-butylaminium fluorosulfon-

ate (12a, 0.56 g, 1.5 mmol) and potassium tert-butoxide61

(28, PCR, Inc., 0.19 g, 1.7 mmol). The system was closed

to the atmosphere, removed from the drybox, and immersed

in an ice bath. Dry hexamethylphosphoramide (Eastman, 10

ml) was added to the stirring solids in an atmosphere of




This material was shown to be Ph2C(OH)CH2S(O)Me,
formally derived from the condensation of sodium dimsylate
and benzophenone: mp 151-152o (lit.60 148-148.5"). Its
nmr spectrum was identical to that of the authentic materi-
al, prepared according to reference 60.









dry nitrogen. The resulting dark red solution was

stirred for two minutes, allowed to warm to room tempera-

ture, and stirred for an additional 4.5 hours, during

which time the solution turned amber. The solvent was

removed at reduced pressure (0.20 mm), and the residue

was treated with carbon tetrachloride. The CCl4 solution

was washed with water and saturated sodium chloride, dried

with anhydrous magnesium sulfate, and concentrated in

vacuo to furnish an oil (0.36 g) whose nmr spectrum

showed a product distribution of 22:9a:Ph2CO::0.4:1:0.8.


Treatment of 12a with Potassium tert-Butoxide (28) in

Ether. A 25-ml round-bottomed flask was placed in a

drybox, and charged with N-(benzhydrylidene)methyl-tert-

butylaminium fluorosulfonate (12a, 0.53 g, 1.5 mmol) and

potassium tert-butoxide (28, freshly sublimed, 0.18 g,

1.6 mmol). The mixture was cooled to -78", and to it was

added (with magnetic stirring) anhydrous ether (10 ml).

The immediate pink color which developed gradually changed

to pale yellow after the mixture had warmed to ambient

temperature. The system was removed from the drybox after

having stirred at 250 for one hour. It was filtered, and

the filtrate was concentrated in vacuo to afford a viscous,

clear, yellow oil (0.33 g) whose NMR SPECTRUM 11 showed a

product ratio of 22:9a:Ph CO::13.4:1.0:2.6.


Preparation and Titration of a Solution of Potassium tert-

Heptoxide (29) in Xylene. Potassium tert-heptoxide (29)









was prepared as a solution in E-xylene, by slight

modification of one of the methods (Method B) of Acharya
62
and Brown. A solution of 3-ethyl-3-pentanol (Aldrich,

97%, 13.94 g, 0.116 mol) and potassium (0.39 g, 0.100

mol) in p-xylene (45 ml) was prepared in a drybox, in

a 100-mi round-bottomed flask. The flask was stoppered,

removed from the drybox, fitted with a reflux condenser

and drying tube, and refluxed for nine hours. The re-

sulting deep red mixture was cooled and filtered in the

drybox to produce a clear, yellow filtrate.

The filtrate was titrated three times, in exactly the

same manner that the sodium bis(trimethylsilyl)amide

solution was assayed videe infra). It was found to be

0.14 M in potassium tert-heptoxide.


Treatment of 12a with Potassium tert-Heptoxide (29). N-

(Benzhydrylidene)methyl-tert-butylaminium fluorosulfonate

(12a, 0.53 g, 1.5 mmol) was stirred magnetically in a 25-

ml round-bottomed flask in a drybox. To it was added the

0.14 M solution of potassium tert-heptoxide (29) in xylene

(12 ml, 1.7 mmol). The resulting amber slurry was stirred

for one hour and then filtered. Upon concentrating in

vacuo, the filtrate afforded a clear, mobile, yellow oil

(0.44 g) whose nmr spectrum showed 22:9a:Ph2CO:Et COH::

13.3:1.0:3.7:15.3.




Note that this color is at variance with the de-
scription in reference 62, which refers to the solution
of 29 as a clear, red liquid.








Sodium Bis(trimethylsilyl)amide (30). Sodium bis(tri-

methylsilyl)amide (30) was prepared by slight modification
14
of the method of Kruger and Niederprum.14 A 500-mi round-

bottomed flask was placed in a drybox and charged with

sodium amide (MC/B, Practical Grade, 19.51 g, 0.500 mol),

hexamethyldisilazane (PCR, Inc., 80.7 g, 104 ml, 0.500

mol), molecular sieves (4A, ca. 10 g), and dry benzene

(250 ml). The flask was stoppered and removed from the

drybox. The black mixture was refluxed for four days, re-

turned to the drybox, and filtered (hot) through Celite.

The clear, colorless filtrate was evaporated to dryness in

vacuo, first with a trapped water aspirator and then with

a vacuum pump (ca. 0.03 mm). Precautions were taken to

exclude moisture from the pure white powder. The sodium

bis(trimethylsilyl)amide (30) was both weighed (81.02 g,

88%) and stored in the drybox.


Preparation and Titration of a Solution of Sodium Bis(tri-

methylsilyl)amide (30) in Benzene. A mixture of sodium

bis(trimethylsilyl)amide (30, 22.01 g, 0.120 mol) and

molecular sieves (4A, ca. 5 g) was stirred in dry benzene

(300 ml) in a drybox until all of the base had dissolved.

The molecular sieves and any insoluble impurities were

separated from the solution by filtration through Celite

in the drybox. The filtrate was diluted with more benzene

(100 ml) and the solution was stored in the drybox in an

amber bottle.

The solution of 30 in benzene was assayed by carefully








measuring three aliquots into 10-ml volumetric flasks,

removing the flasks from the drybox, and quantitatively

transferring their contents to three 100-ml round-

bottomed flasks. Benzene was used to facilitate the

transfer. The diluted aliquots were decomposed with

distilled water (ca. 10 ml), and the resulting mixture

was concentrated to dryness at reduced pressure. The

residual sodium hydroxide was treated with distilled

water (ca. 10 ml) and methyl red indicator (0.1% w/v in

ethanol, 2 drops). In a typical assay, neutralization

of the three samples required 25.9, 26.2, and 26.1 ml of

standard 0.1000 M hydrochloric acid, indicating that the

concentration of sodium bis(trimethylsilyl)amide in the

benzene solution was 0.26(1) molar.


Treatment of 12a with Sodium Bis(trimethylsilyl)amide (30)

in Liquid Sulfur Dioxide. A 25-mi round-bottomed flask

equipped with a magnetic stirrer was placed in a drybox

and charged with N-(benzhydrylidene)methyl-tert-butyl-

aminium fluorosulfonate (12a, 0.53 g, 1.5 mmol) and sodium

bis(trimethylsilyl)amide (30, 0.31 g, 1.7 mmol). The flask

was stoppered with a serum cap, removed from the drybox,

and joined via a hypodermic needle to a flamed vacuum

manifold equipped with a source of dry nitrogen and a

reservoir of liquid sulfur dioxide (dried over phosphorus

pentoxide). The flask was cooled to -78 and liquid sulfur

dioxide (ca. 10 ml) was condensed into it. The resulting








orange slurry was stirred for one hour at -78", after

which time the sulfur dioxide was allowed to evaporate at

room temperature. The residual tan gum was treated with

ether and water, and the separated ethereal layer was

washed with saturated sodium chloride, dried over anhydrous

magnesium sulfate, and evaporated in vacuo. The nmr spec-

trum of the resulting yellow oil (0.08 g) indicated that

N-(benzhydrylidene)tert-butylamine (9a) and benzophenone

were the principal components of the crude product mixture.

The presence of l-tert-butyl-2,2-diphenylaziridine (22) was

not detected in this spectrum.


Treatment of 12a with Sodium Bis(trimethylsilyl)amide (30)

in Various Solvents at 25C. Purification of 1-tert-Butyl-

2,2-diphenylaziridine (22). A mixture of N-(benzhydrylidene)-

methyl-tert-butylaminium fluorosulfonate (12a, 0.53 g, 1.5

mmol) and sodium bis(trimethylsilyl)amide (30, 0.29 g, 1.6

mmol) was stirred magnetically in a 25-ml round-bottomed

flask, in a drybox. The appropriate solvent (10 ml) was

added, and the mixture was stirred at ambient temperature

for one hour. It was then removed from the drybox and

filtered. The filtrate was concentrated in vacuo, and the

residue was weighed and then assayed by careful integration

of its nmr spectrum. The relative distributions of 1-tert-




It was demonstrated in an independent experiment, too,
that NaN(SiMe3)2 is largely insoluble in liquid SO2 at this
concentration.




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